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 · Competitive PvP
Territory control through shooter execution and constant prediction of adapting human teams.

Execution · Competitive PvP
A platform fighter where reading opponents and precise execution both drive victory.
Splatoon leans Execution (Competitive PvP); Super Smash Bros. for Nintendo 3DS leans Execution (Competitive PvP).
Super Smash Bros. for Nintendo 3DS leans a little harder on execution, though the gap is small.
Splatoon
Aim, swim-form movement and ink management are constant demands
Super Smash Bros. for Nintendo 3DS
precise inputs and combo execution required
Super Smash Bros. for Nintendo 3DS leans a little harder on reads, though the gap is small.
Splatoon
Human opponents adapt flanks and pushes every match
Super Smash Bros. for Nintendo 3DS
reading opponent habits and mixups
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Splatoon
Hidden squids in ink create momentary information gaps
Super Smash Bros. for Nintendo 3DS
item spawns add randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Splatoon
Weapon kits, map control timing and gear builds reward study
Super Smash Bros. for Nintendo 3DS
matchup knowledge and combos solvable
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.