head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto: San Andreas demands more optimization; Resistance: Fall of Man demands more reads.

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

Execution · Practiced Mastery
Alternate-history alien-invasion shooter known for its inventive Chimeran arsenal.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Resistance: Fall of Man leans Execution (Practiced Mastery).
Resistance: Fall of Man leans clearly harder on execution.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Resistance: Fall of Man
Aim and weapon handling against Chimera hordes.
Resistance: Fall of Man leans clearly harder on reads.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Resistance: Fall of Man
Sizable competitive multiplayer added genuine human opposition.
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
Resistance: Fall of Man
Campaign unknowns on first pass.
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Resistance: Fall of Man
Exotic weapon selection per encounter rewards system knowledge.
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.