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

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

Execution · Practiced Mastery
Combat racing spin-off where the Jak cast trades platforming for weaponized cars.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Jak X: Combat Racing leans Execution (Practiced Mastery).
Jak X: Combat Racing leans clearly harder on execution.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Jak X: Combat Racing
Drift control while aiming weapons
Jak X: Combat Racing leans clearly harder on reads.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Jak X: Combat Racing
Versus races involve light human jockeying
Jak X: Combat Racing leans a little harder on variance, though the gap is small.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Jak X: Combat Racing
Weapon pickups randomize race swings
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Jak X: Combat Racing
Car tuning and track shortcut 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.