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

Execution · Competitive PvP
Football execution and human mind-games layered over tactical formation play.

Execution · Competitive PvP
Shot timing and play-calling against opponents who scheme around your habits.
International Superstar Soccer Pro 98 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 Pro 98
First-touch timing and finishing demand practiced hands
NBA 2K16
Shot-stick timing and dribble moves gate every possession
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
International Superstar Soccer Pro 98
Versus matches hinge on outguessing a human defender
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 Pro 98
Bounces and deflections add bounded match 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 Pro 98
Formations and set-piece routines have learnable best answers
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.