head to head
Grand Theft Auto V asks more than Harry Potter and the Half-Blood Prince, and the gap is execution.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Optimization · Practiced Mastery
Gentle minigame variety - flying, potions, duels - with no demanding axis.
Grand Theft Auto V leans Execution (Practiced Mastery); Harry Potter and the Half-Blood Prince leans Optimization (Practiced Mastery).
Grand Theft Auto V leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Harry Potter and the Half-Blood Prince
Quidditch ring-chasing and duel timing are gentle
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Harry Potter and the Half-Blood Prince
Duelling NPCs follow simple fixed patterns
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Harry Potter and the Half-Blood Prince
Hogwarts tasks are scripted and repeatable
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Heists, money loops, builds learnable.
Harry Potter and the Half-Blood Prince
Potion-stirring sequences and castle routing are lightly solvable
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.