Description

The concept for this mod is simple; A lot of the vanilla skills are underwhelming and attempting to rebalance combat by just changing weapons falls flat due to how railroaded the playstyles become with just a few perk investments.
With that in mind, this mod goes through the worst offenders and completely changes how they play. See below for some details.

Requirements

Starfield Community Patch : This is not a hard requirement, but several of its keyword and damage calculation fixes are required for intended performance.
Balanced Ballistics (Henceforth, BB) : This is not a hard requirement but these can be considered two modules of the same overhaul. All values are carefully tuned for use with BB.

Compatibility

This mod only touches a few player perks, and in an attempt to retain compatibility, only changes their effects and conditions. Other mods checking for the presence or ranks of these vanilla perks should still function as intended. It is published as a Light Master created in the CK.

Incompatible with comprehensive rebalances or overhauls like Ascension. Pick whichever you prefer.

Deadly Effective is designed to be a tight Vanilla+ experience when combined with other modules like Balanced Ballistics.

Load the mod last to avoid entanglements. Any mods that change the same perks are either soft or hard incompatibilities.

Installation

This can be installed mid-game as it only adds a few new records attached to the vanilla perks in the form of MGEF or SPELs. Perk challenges will technically retain current progress but mileage may vary.

I would not recommend mid-game uninstallation, but it should be mostly safe as no scripts or quests are touched. 

What does Deadly Effective do?

Most of what it does can be seen in the screenshots or in-game - it touches the perks listed below (some are just improved, some are completely overhauled.)
First I will explain the general concept of the mod then what has been changed.

The new gameplay flow is designed to first require the player to select an archetype. Do you want to use automatic weapons and slowly overcome their downsides? Do you want to use the now highly accurate energy weapons and capitalize on their ability to lay down consistent fire? Or do you want to just blitz into a room and clear hostiles in moments? All of these are now available from level one with the new structure. 

However, none of these become obsolete as you gain power and invest into higher level skills. Whether you run traditional long guns, pistols, or shotguns, the later perks will simply build on your effectiveness in combat. Let’s go over them below.

Tier One Perks

These are all viable archetypes to build a playstyle on from level one, instead of being pity selections you regret spending points on later. 

Ballistics is now Neutralisation - the first tier of long-gun specialization. It focuses on semi-automatic carbines but also buffs pistols and shotguns at higher investment.

1 - Semi-Automatic weapons can be fired 15% faster and reloaded 5% faster.
2 - Semi-Automatic weapons are significantly more accurate.
3 - Semi-automatic weapons deal 30% more headshot damage and 20% more torso damage.
4 - Above bonuses apply to Burst-Fire weapons as well as Semi-Auto. 5% chance to ignore enemy armor.

Lasers is now Focus - A broader discipline that covers all energy weapons in the game. It leverages the lack of recoil introduced in BB to capitalize on landing consecutive shots.

1 - Energy weapons do up to 25% more damage upon consecutive hits.
2 - Energy weapon crit chance increases by up to 15% upon consecutive hits.
3 - Energy weapons reload 10% faster and deal 25% more crit damage.
4 - Continuous fire with energy weapons ignores 15% of enemy armor.

Dueling is now Evasion - “The art of avoiding lethal damage and getting close enough to dish it out.”
Cyberpunk Enjoyers may recognize traces of the Mitigation mechanic here. It is designed to make all CQC playstyles viable even at higher difficulties.

1 - Deal 50% more melee damage. Ignore 25% of incoming damage while sprinting.
2 - Ignore 15% of incoming damage while crouched. Above bonuses are doubled.
3 - Melee kills heal you for 15%. Pistol kills heal for 5%.
4 - Move 20% faster with melee weapons or pistols.

Pistol Certification has been modified heavily to encourage a more swashbuckling, daring playstyle. Gunslingers now manipulate enemy health to their advantage and can leverage other perks to become invincible in CQC.

1 - Pistols do 25% more critical damage to enemies with full health and reload 10% faster.
2 - Pistols have a 15% increased chance to critical hit.
3 - 25% chance to ignore damage for 3 seconds after a pistol kill. 
4 - Pistols do 50% more damage to enemies below half health and reload much faster. 

Shotgun Certification now focuses heavily on the strengths of shotguns and their ability to clear rooms with terrifying effectiveness.
Note: The reload speed bonus now scales with skill rank. This will eventually be applied to most certifications.

1 - Shotguns do 15% more damage and reload 10% faster.
2 - Torso shots with shotguns have a chance to stun.
3 - Non-standard shotshells like Slugs and Flechettes are 30% more effective.
4 - Shotguns have 15% increased range and deal 40% more critical damage with non-headshots.

Tier Two Perks

Rifle Certification is now Suppression - all non-certification perks are designed to build on classic long-gun combat. Therefore, this perk focuses on automatic weapon effectiveness.

1 - Automatic weapons can be reloaded 5% faster and deal 10% more damage.
2 - Automatic weapon spread can be controlled effectively. (balanced around BB’s new debuffs to automatic fire.)
3 - Automatic weapons are up to 40% more effective within 15 meters.
4 - Resist up to 40% of damage while continuously landing hits with automatic weapons. (This is to simulate suppressive fire. I am open to superior methods.)

Incapacitation now differentiates between organic and inorganic targets.

1 - EM weapons do 40% more damage to organic targets.
2 - EM weapons do 30% more damage to inorganic targets.
3 - Reload EM weapons 5% faster. EM weapons deal 10% additional damage to all targets.
4 - EM weapons have a 5% chance to instantly KO human targets.

Particle Beams is replaced by Efficiency - the concept being that a savvy technician can squeeze enormous efficiency out of initially underperforming weapons.

1 - All energy weapons do 15% more damage.
2 - All non-standard energy types ignore 15% of armor (Note: This includes everything but Lasers.)
3 - Energy weapons using standard ammunition fire two shots per trigger pull. (Note: This excludes Ignition Beams.)
4 - Energy weapons can be reloaded 15% faster.

Demolitions has been simply tweaked to be more effective with less investment.

1 - Unchanged from vanilla.
2 - Explosives deal 50% more damage. Resist 25% of explosive damage.
3 - Weapons firing explosive rounds have a 10% chance to knock down the target.
4 - Explosions have a 50% larger radius. Resist 50% of explosive damage.

Tier Three Perks

Rapid Reloading is now Weapon Handling. I was greatly perturbed by the possibility of having to invest three perk points to get a minor buff for my weapon of choice in some cases.

1 - Reload all weapons 15% faster.
2 - Reload all weapons 30% faster. Move 15% faster in combat with long guns.
3 - Chance on hitting enemies to increase reload speed for all weapons by 50% for 15 seconds.
4 - Reloading is uninterruptible.

Synergies

Obviously, several new playstyles are opened up by cleverly combining the new perks, but here I will explain a few that I had in mind when creating the mod.

Vaquero
Utilizes Neutralisation, Pistol Certification, and Evasion. A deadly gunslinger that is nearly untouchable when in the midst of enemies, favoring high-crit and high-damage pistols and falling back on knives or axes to finish off foes.

Trench Gunner
Utilizes Suppression, Shotgun Certification, and Weapon Handling. A master of CQC whose enemies rarely have time to react before being blown to bits by shotshells of all kinds.

Space Marine
No, not that kind! Utilizes Suppression, Weapon Handling, and Focus to lay down reams of highly accurate and deadly lasgun energy fire, quickly eliminating all threats before giving his (or her) team the all-clear. 

Credits

Bethesda Softworks for Starfield and the CK, flawed masterpieces both may be.
ElminsterAU for xEdit which allowed BB to exist well in advance of official tooling.
This project builds upon my own Balanced Ballistics which in turn originally built upon ASARDE - thanks to cheesemongler for (to my knowledge) being the first to delve into damage and balance calculations for auto and semi-auto weaponry in Starfield.
Drop him some kudos and endorsements if you enjoyed BB or DE.

Spacefarer - A Modular Overhaul

Most of my mods so far have been designed to work as a modular and compatible vanilla+ series - Hereby dubbed Spacefarer.
Check them out if you're interested!

Combat
Deadly Effective - Overhauls the blandest vanilla combat perks for playstyle diversity (and fun!)
Balanced Ballistics - Highlights the strengths and weaknesses of various weapon types.
Suit Up - Smart and compatible categorization for vanilla armors.
Space Economy
Cost of Spacing - Simulates a complex space economy by introducing costs to space travel in a lightweight manner.
Spacefaring Economy - Overhauls prices and rewards with heavy scaling to avoid hyperinflation.
Captain’s Choice - Rebalances ship classes and modules for more thoughtful shipbuilding and combat.
Immersion
No More Magic Boost Packs - This is probably my personal favorite. You can’t boost jump unless you are visibly wearing a boost pack.
Immersive Renames [RTFP] - Renames a variety of mod-added items to meet vanilla naming conventions.