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
Tests quick ball control and outguessing a human defender's tackles.

Execution · Competitive PvP
Shot timing and play-calling against opponents who scheme around your habits.
International Superstar Soccer Deluxe leans Execution (Competitive PvP); NBA 2K16 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.
International Superstar Soccer Deluxe
Pass and shot timing under pressure decide matches
NBA 2K16
Shot-stick timing and dribble moves gate every possession
International Superstar Soccer Deluxe leans a little harder on reads, though the gap is small.
International Superstar Soccer Deluxe
Versus a human, faking runs and reading tackles is central
NBA 2K16
Online opponents adjust defensive schemes against your tendencies
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
International Superstar Soccer Deluxe
Deflections and keeper bounces add light chaos
NBA 2K16
Shot RNG and card packs add bounded randomness
NBA 2K16 leans a little harder on optimization, though the gap is small.
International Superstar Soccer Deluxe
Formations and set-piece routines are learnable systems
NBA 2K16
Playbooks, rotations and roster building reward deep 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.