I half joked about this on another page but if you wanted him beefed up to remain relevant and be a counter to Luke, his kit could look something like this. Isn't stupidly overpowered because most new characters are overpowered in their own right and this is a mirror to CLS. Just a bit of fun. The idea is he gets stronger the longer he fights and is very anti rebel/Jedi like in the story.
Darth Vader
Terrifying Swing (Basic) Omega'd
Deal Physical damage to target enemy, inflict Ability Block for 1 Turn and 50% chance to dispel all buffs. Jedi and Rebel targets cannot Evade or Resist the effects of this attack. If resisted, deal double damage.
Force Crush (Special) Omega'd
'4 Turn Cooldown'
Deal Physical damage to all enemies and inflict Speed Down, Health Down and 3 Damage Over Time effects for 2 rounds. For each enemy that resists, deal +20% damage and recover 10% health.
Culling Blade (Special) Omega'd
'3 Turn Cooldown'
Deal Physical damage to target enemy and dispels all negative status effects on them. This attack deals 50% more damage for each effect dispelled, grants 100% Turn Meter and recovers 100% protection on a finishing blow. This attack can't be evaded.
Inspiring Through Fear (Leader) Zeta'd
Empire and Sith allies gain 30% Offense, +30% Critical Damage, +15% Critical Chance and have a 50% chance to remove 25% Turn Meter on hit. This Turn Meter removal can't be Resisted. While Darth Vader is alive, enemies immediately regain Damage Over Time for 2 turns whenever Damage Over Time expires on them.
Overwhelming Force (Unique) Zeta'd
Darth Vader has 100% turn meter at the start of battle and gains +10% offence after each of his turns, stacking up to +100%. Additionally, he gains +20% defence any time he is attacked, stacking up to +200% and gains +5 speed for each Empire or Sith ally and +3 speed for each debuffed enemy.
Empires Enforcer (Unique) Zeta'd
Rebel and Jedi enemies deal -30% damage to Darth Vader and grant him 10% Turn Meter whenever they attack him. If an enemy lands a Critical Hit on Darth Vader, he gains Offence Up, Defence Up, Speed Up and Critical Chance Up for 1 turn.