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
Shot timing and play-calling against opponents who scheme around your habits.

Execution · Practiced Mastery
A team shooter where aim and positioning against human opponents controls the map.
NBA 2K16 leans Execution (Competitive PvP); Splatoon 2 leans Execution (Practiced Mastery).
Splatoon 2 leans a little harder on execution, though the gap is small.
NBA 2K16
Shot-stick timing and dribble moves gate every possession
Splatoon 2
aim and movement decide ink battles
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K16
Online opponents adjust defensive schemes against your tendencies
Splatoon 2
predicting human opponent positioning
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K16
Shot RNG and card packs add bounded randomness
Splatoon 2
weapon and map rotation randomness
Splatoon 2 leans a little harder on optimization, though the gap is small.
NBA 2K16
Playbooks, rotations and roster building reward deep study
Splatoon 2
loadout and turf strategy 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.