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

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

Execution · Practiced Mastery
A platform of millions of user-created multiplayer games spanning every genre, played mostly by younger audiences.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Roblox leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Roblox
Many popular experiences are obby/PvP tests of hands
Roblox leans clearly harder on reads.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Roblox
Multiplayer experiences pit you against other kids' minds
Roblox leans a little harder on variance, though the gap is small.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Roblox
User-generated content means constant unknown systems
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Roblox
Grind economies and trading reward system mastery
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.