head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Ratchet & Clank: Rift Apart demands more optimization.

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

Optimization · Practiced Mastery
Dimension-hopping spectacle platformer built on the classic arsenal-upgrade loop.
Grand Theft Auto V leans Execution (Practiced Mastery); Ratchet & Clank: Rift Apart leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Ratchet & Clank: Rift Apart
Dodging, rift-tether mobility, and weapon aim.
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Ratchet & Clank: Rift Apart
Scripted enemies and setpieces only.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Some mission and lobby randomness.
Ratchet & Clank: Rift Apart
Unknown encounters on first run.
Ratchet & Clank: Rift Apart leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Ratchet & Clank: Rift Apart
Weapon leveling and bolt economy reward planned play.
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.