head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is variance, and it is a single point.

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

Execution · Practiced Mastery
A movie tie-in testing combo timing against scripted duels.
Grand Theft Auto V leans Execution (Practiced Mastery); Star Wars: Episode III - Revenge of the Sith leans Execution (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.
Star Wars: Episode III - Revenge of the Sith
Lightsaber combos and blocks need modest timing
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Star Wars: Episode III - Revenge of the Sith
Versus duel mode adds light human prediction
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Star Wars: Episode III - Revenge of the Sith
Encounters are fixed movie-scripted setpieces
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Heists, money loops, builds learnable.
Star Wars: Episode III - Revenge of the Sith
Combo unlocks and boss patterns are quickly mapped
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.