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.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.

Execution · Practiced Mastery
Open-world western about an outlaw forced to hunt down his old gang.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Red Dead Redemption leans Execution (Practiced Mastery).
Red Dead Redemption leans a little harder on execution, though the gap is small.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Red Dead Redemption
Dead Eye softens but gunplay still wants aim
Red Dead Redemption leans a little harder on reads, though the gap is small.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Red Dead Redemption
Multiplayer skirmishes add light human prediction
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Red Dead Redemption
Ambient events and spawns vary mildly
Grand Theft Auto: San Andreas leans a little harder on optimization, though the gap is small.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Red Dead Redemption
Mission approaches and economy are 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.