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

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

Execution · Practiced Mastery
Tests arcade sports timing in a licensed fantasy sport with swingy Snitch catches.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Harry Potter: Quidditch World Cup leans Execution (Practiced Mastery).
Harry Potter: Quidditch World Cup leans a little harder on execution, though the gap is small.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Harry Potter: Quidditch World Cup
Timing passes, tackles and Snitch chases needs moderate dexterity
Harry Potter: Quidditch World Cup leans clearly harder on reads.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Harry Potter: Quidditch World Cup
Versus a friend, faking plays adds light prediction
Harry Potter: Quidditch World Cup leans a little harder on variance, though the gap is small.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Harry Potter: Quidditch World Cup
Snitch appearances and combo opportunities add swing
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Harry Potter: Quidditch World Cup
Special move charging and team choice reward system 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.