head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Kingdom Hearts 358/2 Days demands more optimization.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Optimization · Practiced Mastery
Action-RPG combat where the panel-grid loadout puzzle matters more than reflexes.
Grand Theft Auto V leans Execution (Practiced Mastery); Kingdom Hearts 358/2 Days leans Optimization (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Kingdom Hearts 358/2 Days
Real-time keyblade combat with modest timing demands
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Kingdom Hearts 358/2 Days
Heartless and bosses run fixed patterns
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Kingdom Hearts 358/2 Days
Loot drops add minor randomness to gearing
Kingdom Hearts 358/2 Days leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Kingdom Hearts 358/2 Days
The panel grid system rewards careful build planning
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.