head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Competitive PvP
Stick precision and constant prediction of a human opponent's tactical habits.

Execution · Competitive PvP
Movement-heavy shooting where map control and reading enemy pushes decide matches.
Pro Evolution Soccer 2015 leans Execution (Competitive PvP); Splatoon 3 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.
Pro Evolution Soccer 2015
First touch, through-ball timing and finishing demand precise sticks
Splatoon 3
Aim, squid movement and ink mobility decide engagements
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Pro Evolution Soccer 2015
Human opponents bait, switch tactics and punish habits
Splatoon 3
Turf and ranked battles hinge on predicting adapting human squads
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Pro Evolution Soccer 2015
Deflections and referee calls add bounded chaos
Splatoon 3
Matchmaking and special timing add modest noise
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Pro Evolution Soccer 2015
Formations, player roles and set pieces reward study
Splatoon 3
Gear builds, weapon kits and map control patterns are studied
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.