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 · Practiced Mastery
Zero awakens to lead a resistance in a harsh, rank-graded GBA action series debut.

Execution · Practiced Mastery
Movement execution and route optimisation through a fixed, mappable planet.
Mega Man Zero leans Execution (Practiced Mastery); Super Metroid leans Execution (Practiced Mastery).
Mega Man Zero leans a little harder on execution, though the gap is small.
Mega Man Zero
Punishing GBA action with strict ranking on damage
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 Zero
All bosses are pattern-based
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 Zero
Cyber-elf locations hidden at first
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 Zero
Rank system penalises elf use, rewarding optimised clean runs
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.