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

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

Execution · Practiced Mastery
An endless runner starring Sonic and friends.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Sonic Runners Adventure leans Execution (Practiced Mastery).
Sonic Runners Adventure leans clearly harder on execution.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Sonic Runners Adventure
precise timing jumps and dashes at speed
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 Runners Adventure
no adaptive opponent, solo endless runner
Sonic Runners Adventure leans a little harder on variance, though the gap is small.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Sonic Runners Adventure
obstacle and item layouts randomized
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 Runners Adventure
character and item upgrade optimization
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.