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

Execution · Practiced Mastery
The trilogy capper adding a Batmobile to the familiar freeflow formula.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Batman: Arkham Knight leans Execution (Practiced Mastery); Grand Theft Auto V 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.
Batman: Arkham Knight
Combat and Batmobile control need timing.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans a little harder on reads, though the gap is small.
Batman: Arkham Knight
Scripted enemy AI.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Batman: Arkham Knight
Deterministic encounters.
Grand Theft Auto V
Some mission and lobby randomness.
Batman: Arkham Knight leans a little harder on optimization, though the gap is small.
Batman: Arkham Knight
Gadget chains and tank routes learnable.
Grand Theft Auto V
Heists, money loops, builds learnable.
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.