head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

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

Optimization · Practiced Mastery
A four-player Wii Kirby romp gathering ship parts for the stranded alien Magolor.
Harry Potter and the Half-Blood Prince leans Optimization (Practiced Mastery); Kirby's Return to Dream Land leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Harry Potter and the Half-Blood Prince
Quidditch ring-chasing and duel timing are gentle
Kirby's Return to Dream Land
Easygoing main game; EX mode adds modest demands
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
Kirby's Return to Dream Land
Bosses are pattern-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
Kirby's Return to Dream Land
Energy sphere hiding spots are static secrets
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
Kirby's Return to Dream Land
Super ability timing and sphere collection are 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.