head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto: San Andreas demands more optimization; Sonic the Hedgehog (2006) demands more execution.

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

Execution · Practiced Mastery
The infamous, glitch-ridden 2006 Sonic reboot where the physics are the real boss.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Sonic the Hedgehog (2006) leans Execution (Practiced Mastery).
Sonic the Hedgehog (2006) leans clearly harder on execution.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Sonic the Hedgehog (2006)
Fighting unreliable physics demands constant correction
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Sonic the Hedgehog (2006)
No adaptive 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
Sonic the Hedgehog (2006)
Bugs make outcomes partly unpredictable
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Sonic the Hedgehog (2006)
Learning which routes the jank permits
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.