head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Kirby's Star Stacker demands more execution.

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

Execution · Practiced Mastery
A falling-block puzzle testing fast placement and chain-clear setups under pressure.
Grand Theft Auto V leans Execution (Practiced Mastery); Kirby's Star Stacker leans Execution (Practiced Mastery).
Kirby's Star Stacker leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Kirby's Star Stacker
Fast block placement under rising pressure demands speed
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Kirby's Star Stacker
Solo puzzle with no opponent to model
Kirby's Star Stacker leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
Kirby's Star Stacker
Falling-block sequence is random but rapidly mappable
Kirby's Star Stacker leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Kirby's Star Stacker
Setting up cascading star clears is the strategy layer
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.