head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Skul: The Hero Slayer demands more execution.

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

Execution · Practiced Mastery
Head-swapping action roguelite where each skull is a new moveset.
Grand Theft Auto V leans Execution (Practiced Mastery); Skul: The Hero Slayer leans Execution (Practiced Mastery).
Skul: The Hero Slayer leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Skul: The Hero Slayer
Action platforming with skull swaps demands precise combos.
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Skul: The Hero Slayer
Enemy AI is fully scripted.
Skul: The Hero Slayer leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
Skul: The Hero Slayer
Skull and item drops swing runs.
Skul: The Hero Slayer leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Skul: The Hero Slayer
Skull synergies and boss patterns reward study.
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.