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 · Grand Arena
A tag-team 3D fighter layering team optimization onto Tekken's execution and reads core.

Execution · Competitive PvP
KOF's jump to 3D visuals with a huge fifty-character launch roster.
Tekken Tag Tournament leans Execution (Grand Arena); The King of Fighters XIV leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Tekken Tag Tournament
Tag combos and netsu juggles demand precise inputs
The King of Fighters XIV
Max mode confirms and hop pressure test hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Tekken Tag Tournament
Tag timing adds another layer of human mind-games
The King of Fighters XIV
Classic KOF human mixups demand continual reading
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Tekken Tag Tournament
Open information; nothing hidden between rounds
The King of Fighters XIV
Deterministic 3v3 combat
Tekken Tag Tournament leans a little harder on optimization, though the gap is small.
Tekken Tag Tournament
Team synergy and tag combo routing are optimizable systems
The King of Fighters XIV
Team order and max-mode damage routes are studied
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.