head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto: San Andreas demands more optimization; No More Heroes demands more execution.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Execution · Practiced Mastery
Punk action game about an otaku assassin climbing a ranked killer leaderboard.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); No More Heroes leans Execution (Practiced Mastery).
No More Heroes leans clearly harder on execution.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
No More Heroes
Beam katana clashes and wrestling throws with motion timing
No More Heroes leans a little harder on reads, though the gap is small.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
No More Heroes
Assassins are scripted boss fights
Grand Theft Auto: San Andreas leans a little harder on variance, though the gap is small.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
No More Heroes
Deterministic encounters
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
No More Heroes
Boss pattern learning and money grinding
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.