head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is optimization, and it is a single point.

Execution · Practiced Mastery
The 32-bit X series highlight where Zero becomes fully playable with his own saber-based campaign.

Execution · Practiced Mastery
Movement execution and route optimisation through a fixed, mappable planet.
Mega Man X4 leans Execution (Practiced Mastery); Super Metroid 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 X4
Dash-jump mobility and Zero's saber combos test hands
Super Metroid
Wall-jumps, shinesparks and boss dodges demand precise inputs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mega Man X4
Mavericks follow fixed scripts
Super Metroid
Bosses cycle fixed patterns, never adapting
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mega Man X4
Upgrade capsule locations hidden initially
Super Metroid
Item and route knowledge is fixed once discovered
Super Metroid leans a little harder on optimization, though the gap is small.
Mega Man X4
Armor parts, weakness order, and X-vs-Zero routing
Super Metroid
Sequence-breaking route optimisation is the enduring meta-game
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.