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
The 3DS remake of Metroid II built around a precisely timed melee counter.

Execution · Practiced Mastery
A third-person action platformer where you blast scripted alien hordes while leveling an arsenal of gadgets.
Metroid: Samus Returns leans Execution (Practiced Mastery); Ratchet & Clank: Into the Nexus 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.
Metroid: Samus Returns
Melee-counter timing defines nearly every fight.
Ratchet & Clank: Into the Nexus
Aiming, strafing, and platforming under fire carry combat
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Metroid: Samus Returns
Counters punish scripted lunges, not adaptation.
Ratchet & Clank: Into the Nexus
Scripted enemy waves; no adaptive opponent
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Metroid: Samus Returns
Fixed map and encounters.
Ratchet & Clank: Into the Nexus
Fixed level layouts, minimal hidden information
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Metroid: Samus Returns
Aeion management and ability routing matter.
Ratchet & Clank: Into the Nexus
Weapon upgrade paths, bolt economy, gold bolt routing
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.