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

Execution · Practiced Mastery
An anthology of bite-sized Kirby adventures with deep copy abilities and co-op helpers.

Execution · Practiced Mastery
A linear, cinematic Metroid mixing third-person action with first-person aiming.
Kirby Super Star leans Execution (Practiced Mastery); Metroid: Other M leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby Super Star
Helper juggling and The Arena demand competence
Metroid: Other M
Dodge-timing and pointer-switch finishers
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby Super Star
Pattern-based bosses throughout
Metroid: Other M
Bosses run scripted patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby Super Star
Treasure locations in Great Cave are fixed
Metroid: Other M
Linear, deterministic encounters
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby Super Star
Ability matchups and boss patterns reward learning
Metroid: Other M
Learning boss movesets and item routes
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.