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
A charming kid-friendly RPG with timing prompts and light costume strategy.

Optimization · Practiced Mastery
An easygoing co-op Kirby about recruiting enemies as friends and combining their elemental powers.
Costume Quest leans Optimization (Practiced Mastery); Kirby Star Allies 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.
Costume Quest
Timed button prompts are the only dexterity ask
Kirby Star Allies
Very low difficulty, AI allies carry fights
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Costume Quest
Monster battles follow simple fixed scripts
Kirby Star Allies
Friend AI helps rather than opposes
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Costume Quest
Quest content is fixed once doors are knocked
Kirby Star Allies
Fixed layouts and bosses
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Costume Quest
Costume ability matchups and stamp choices are light strategy
Kirby Star Allies
Friend-ability element combos solve puzzles
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.