head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Optimization · Practiced Mastery
Gentle minigame variety - flying, potions, duels - with no demanding axis.

Execution · Practiced Mastery
Linear postwar crime story driven by cover shootouts and atmosphere.
Harry Potter and the Half-Blood Prince leans Optimization (Practiced Mastery); Mafia II leans Execution (Practiced Mastery).
Mafia II leans a little harder on execution, though the gap is small.
Harry Potter and the Half-Blood Prince
Quidditch ring-chasing and duel timing are gentle
Mafia II
Cover shooting and fistfight timing
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Harry Potter and the Half-Blood Prince
Duelling NPCs follow simple fixed patterns
Mafia II
Enemies are scripted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Harry Potter and the Half-Blood Prince
Hogwarts tasks are scripted and repeatable
Mafia II
Story missions are fixed
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Harry Potter and the Half-Blood Prince
Potion-stirring sequences and castle routing are lightly solvable
Mafia II
Modest; learning encounter layouts
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.