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.

Execution · Pure Mechanics
A run-and-gun boss rush about dodging scripted patterns with tight inputs.

Execution · Practiced Mastery
Tight platforming execution against fixed boss patterns with a solvable upgrade route.
Cuphead leans Execution (Pure Mechanics); Mega Man X3 leans Execution (Practiced Mastery).
Cuphead leans a little harder on execution, though the gap is small.
Cuphead
Tight dodging and parry timing decide every boss.
Mega Man X3
Dash-jump precision and boss dodging demand tight inputs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Cuphead
Bosses cycle scripted phases; no adaptation to player.
Mega Man X3
Mavericks cycle fixed attack patterns
Cuphead leans a little harder on variance, though the gap is small.
Cuphead
Minor attack-order shuffling between phases.
Mega Man X3
Nothing random - every pickup and enemy is placed
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Cuphead
Loadouts and boss phase order are fully learnable.
Mega Man X3
Weapon-order and upgrade routing is a known solved sequence
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.