head to head
Neither is simply harder - they are hard in different places. Alien demands more execution; Grand Theft Auto: San Andreas demands more optimization.

Execution · Practiced Mastery
A Pac-Man-style routing and dodging test wearing an Alien license.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Alien leans Execution (Practiced Mastery); Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery).
Alien leans clearly harder on execution.
Alien
Maze dodging under drone pursuit is pure timing
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Alien
Drones chase with simple fixed logic, nothing adaptive
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Alien
Drone movements vary slightly per attempt
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Alien
Optimal egg-clearing routes are quickly mappable, Pac-Man style
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.