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
Punishing platforming execution over learnable boss orders and part builds.

Execution · Practiced Mastery
Bullet-hell metroidvania whose bunny-girl bosses fill the screen with patterns.
Mega Man X6 leans Execution (Practiced Mastery); Rabi-Ribi 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.
Mega Man X6
Cruel platforming and boss windows demand frame-tight inputs
Rabi-Ribi
Dense bullet-hell boss patterns demand precise dodging.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mega Man X6
Bosses are fixed pattern sets
Rabi-Ribi
Boss patterns are fixed and memorizable.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mega Man X6
The Nightmare System shuffles level hazards between runs
Rabi-Ribi
Exploration unknowns on first run.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mega Man X6
Weapon orders, armor parts and route knowledge are essential
Rabi-Ribi
Sequence-breaking routes and boss pattern study converge to mastery.
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.