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

Execution · Competitive PvP
Mechanical football execution plus reading a human opponent's meta habits.

Execution · Competitive PvP
Arcade tennis with timing-based PvP mind games.
FIFA 19 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 19
Skill moves and timed finishing reward fast hands
Mario Tennis Aces
Shot timing, charge mechanics, footwork
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA 19
Ranked opponents adapt; baiting their defending is prediction
Mario Tennis Aces
Online tennis demands reading opponent placement
FIFA 19 leans a little harder on variance, though the gap is small.
FIFA 19
Finishing RNG and deflections decide tight margins
Mario Tennis Aces
Mostly deterministic ball physics
FIFA 19 leans a little harder on optimization, though the gap is small.
FIFA 19
Meta formations and chemistry are solvable homework
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.