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

Execution · Competitive PvP
Twitch ball control plus constant prediction of human defenders on known maps.
International Superstar Soccer Deluxe leans Execution (Competitive PvP); TagPro leans Execution (Competitive PvP).
TagPro leans a little harder on execution, though the gap is small.
International Superstar Soccer Deluxe
Pass and shot timing under pressure decide matches
TagPro
Ball handling, boosts and juke precision decide grabs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
International Superstar Soccer Deluxe
Versus a human, faking runs and reading tackles is central
TagPro
Human defenders adapt to your routes every match
International Superstar Soccer Deluxe leans a little harder on variance, though the gap is small.
International Superstar Soccer Deluxe
Deflections and keeper bounces add light chaos
TagPro
Maps and power-up timers are fully visible
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
International Superstar Soccer Deluxe
Formations and set-piece routines are learnable systems
TagPro
Map routes, button plays and power-up timing are studyable
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.