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

Execution · Practiced Mastery
An open-city sequel deepening freeflow combat and predator gadget play.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Batman: Arkham City leans Execution (Practiced Mastery); Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery).
Batman: Arkham City leans a little harder on execution, though the gap is small.
Batman: Arkham City
Combo chains and counters need timing.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Batman: Arkham City leans a little harder on reads, though the gap is small.
Batman: Arkham City
Enemies scripted, not adaptive.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Grand Theft Auto: San Andreas leans a little harder on variance, though the gap is small.
Batman: Arkham City
Fixed encounters and challenges.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Grand Theft Auto: San Andreas leans a little harder on optimization, though the gap is small.
Batman: Arkham City
Gadget combos and challenge maps learnable.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic 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.