head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is optimization, and it is a single point.

Execution · Competitive PvP
A combo-centric fighting game built around the breaker guessing game.

Execution · Grand Arena
A tag-team 3D fighter layering team optimization onto Tekken's execution and reads core.
Killer Instinct leans Execution (Competitive PvP); Tekken Tag Tournament leans Execution (Grand Arena).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Killer Instinct
Long combo execution and breaker timing
Tekken Tag Tournament
Tag combos and netsu juggles demand precise inputs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Killer Instinct
Combo-breaker guessing is a live mind game
Tekken Tag Tournament
Tag timing adds another layer of human mind-games
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Killer Instinct
Full information fighter
Tekken Tag Tournament
Open information; nothing hidden between rounds
Tekken Tag Tournament leans a little harder on optimization, though the gap is small.
Killer Instinct
Frame data and matchup study
Tekken Tag Tournament
Team synergy and tag combo routing are optimizable systems
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.