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

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

Execution · Competitive PvP
The Wii U Smash that restored competitive pace and a huge roster of labbable kill confirms.
Splatoon leans Execution (Competitive PvP); Super Smash Bros. for Wii U 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.
Splatoon
Aim, swim-form movement and ink management are constant demands
Super Smash Bros. for Wii U
Perfect pivots and precise aerial spacing reward sharp hands.
Super Smash Bros. for Wii U leans a little harder on reads, though the gap is small.
Splatoon
Human opponents adapt flanks and pushes every match
Super Smash Bros. for Wii U
Ledge-trap and landing-trap guessing against humans never converges.
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 Wii U
Tripping removed; only minor move RNG remains.
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 Wii U
Rage mechanics and kill-confirm percents are deeply labbable.
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.