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

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

Execution · Practiced Mastery
Careful climbing execution and route planning where a single mistimed grab undoes everything.
Grand Theft Auto V leans Execution (Practiced Mastery); Peak leans Execution (Practiced Mastery).
Peak leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Peak
Stamina-managed grip timing - one slipped input drops the whole climb
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Peak
Co-op against a mountain, no adaptive opponent
Peak leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Peak
Daily map rotation and item spawns shuffle each ascent
Peak leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Peak
Routing the wall and rationing items decides summit attempts
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.