head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Wario Land 4 demands more execution.

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

Execution · Practiced Mastery
GBA platformer where Wario smashes through puzzle levels and races escape timers for treasure.
Grand Theft Auto V leans Execution (Practiced Mastery); Wario Land 4 leans Execution (Practiced Mastery).
Wario Land 4 leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Wario Land 4
Frantic escape sequences demand tight platforming under timers
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Wario Land 4
Fixed scripted levels with no adaptive opposition
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Wario Land 4
Layouts fixed; only first-run secret discovery
Wario Land 4 leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Wario Land 4
Treasure routing and frog-switch timing reward 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.