head to head
Neither is simply harder - they are hard in different places. Driv3r demands more execution; Grand Theft Auto: San Andreas demands more optimization.

Execution · Practiced Mastery
White-knuckle chase driving and route memorisation through punishing scripted missions.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Driv3r leans Execution (Practiced Mastery); Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery).
Driv3r leans clearly harder on execution.
Driv3r
Unforgiving chase driving and clunky on-foot shooting demand control
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.
Driv3r
Pursuers follow fixed AI logic
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.
Driv3r
Traffic adds noise to chases, missions are scripted
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Driv3r
Memorising city routes and mission scripts carries completion
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.