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
Late-90s arcade football execution with couch-versus prediction and bouncy luck.

Execution · Competitive PvP
Execution on the ball plus constant prediction of the other player's shape.
FIFA 99 leans Execution (Competitive PvP); Pro Evolution Soccer 2009 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.
FIFA 99
Quick passing and shot timing in arcade-leaning football
Pro Evolution Soccer 2009
Close control and finishing windows demand stick precision
Pro Evolution Soccer 2009 leans a little harder on reads, though the gap is small.
FIFA 99
Couch opponents can be conditioned and baited
Pro Evolution Soccer 2009
Online and couch opponents adjust tactics against you
FIFA 99 leans a little harder on variance, though the gap is small.
FIFA 99
Era physics produce regular fluke goals
Pro Evolution Soccer 2009
Ricochets and keeper parries add small randomness
Pro Evolution Soccer 2009 leans a little harder on optimization, though the gap is small.
FIFA 99
Simple formations and known exploit angles map fast
Pro Evolution Soccer 2009
Squad setup and tactical sliders reward preparation
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.