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
Classic licensed football testing input control and opponent pattern reading.

Execution · Competitive PvP
Arcade tennis with timing-based PvP mind games.
FIFA Soccer 2005 leans Execution (Competitive PvP); Mario Tennis Aces 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 Soccer 2005
Off-the-ball control and finishing timing are mechanical skill
Mario Tennis Aces
Shot timing, charge mechanics, footwork
Mario Tennis Aces leans a little harder on reads, though the gap is small.
FIFA Soccer 2005
Human opponents adjust attack patterns across a match
Mario Tennis Aces
Online tennis demands reading opponent placement
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA Soccer 2005
Bounces and keeper behaviour add minor chaos
Mario Tennis Aces
Mostly deterministic ball physics
FIFA Soccer 2005 leans a little harder on optimization, though the gap is small.
FIFA Soccer 2005
Formations and exploit plays of the era are learnable
Mario Tennis Aces
Character matchups and tech routes
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.