head to head
Neither is simply harder - they are hard in different places. Dragon Ball: Revenge of King Piccolo demands more execution; Grand Theft Auto: San Andreas demands more optimization.

Execution · Practiced Mastery
A licensed brawler testing combat timing and memorised boss patterns.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Dragon Ball: Revenge of King Piccolo leans Execution (Practiced Mastery); Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery).
Dragon Ball: Revenge of King Piccolo leans clearly harder on execution.
Dragon Ball: Revenge of King Piccolo
Combo timing and platforming reflexes carry the levels
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Dragon Ball: Revenge of King Piccolo leans a little harder on reads, though the gap is small.
Dragon Ball: Revenge of King Piccolo
Bosses run scripted patterns, never adapt
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Grand Theft Auto: San Andreas leans a little harder on variance, though the gap is small.
Dragon Ball: Revenge of King Piccolo
Level content is fixed after one playthrough
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Dragon Ball: Revenge of King Piccolo
Learning boss movesets and stage routes is the rest
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.