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

Execution · Competitive PvP
The toned-down crossover fighter matching Mortal Kombat's roster against DC superheroes.

Execution · Competitive PvP
Territory control through shooter execution and constant prediction of adapting human teams.
Mortal Kombat vs. DC Universe leans Execution (Competitive PvP); Splatoon leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat vs. DC Universe
Juggle combos and klose kombat timing
Splatoon
Aim, swim-form movement and ink management are constant demands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat vs. DC Universe
Human mixups, though a simpler toolset than peers
Splatoon
Human opponents adapt flanks and pushes every match
Splatoon leans a little harder on variance, though the gap is small.
Mortal Kombat vs. DC Universe
Deterministic crossover combat
Splatoon
Hidden squids in ink create momentary information gaps
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat vs. DC Universe
Mapping juggle routes and matchup tools rewards practice
Splatoon
Weapon kits, map control timing and gear builds reward study
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.