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
Shot-timing execution against adapting human defense, on top of build and playbook math.

Execution · Competitive PvP
Territory control through shooter execution and constant prediction of adapting human teams.
NBA 2K17 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.
NBA 2K17
Shot meter timing and dribble execution decide possessions
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.
NBA 2K17
Online opponents adapt defensive schemes and bait plays
Splatoon
Human opponents adapt flanks and pushes every match
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K17
Shot RNG wraps the timing meter
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.
NBA 2K17
Build math, playbooks and matchup hunting underpin wins
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.