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

Execution · Practiced Mastery
A colorful co-op beat-em-up with light RPG progression.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Castle Crashers Remastered leans Execution (Practiced Mastery); Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery).
Castle Crashers Remastered leans clearly harder on execution.
Castle Crashers Remastered
combo timing in co-op brawler combat
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Castle Crashers Remastered leans a little harder on reads, though the gap is small.
Castle Crashers Remastered
enemies scripted, no real adaptation
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.
Castle Crashers Remastered
weapon and magic drop randomness
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Castle Crashers Remastered
leveling and weapon choices are learnable
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.