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 · Pure Mechanics
Famously unforgiving ball control tested against human prediction in fast matches.

Execution · Competitive PvP
Arcade tennis with timing-based PvP mind games.
Kick Off 2 leans Execution (Pure Mechanics); Mario Tennis Aces leans Execution (Competitive PvP).
Kick Off 2 leans a little harder on execution, though the gap is small.
Kick Off 2
The ball never sticks - constant trapping demands famously precise control
Mario Tennis Aces
Shot timing, charge mechanics, footwork
Mario Tennis Aces leans a little harder on reads, though the gap is small.
Kick Off 2
Human matches reward predicting passes and tackle timing
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.
Kick Off 2
Pitch types and deflections add mild chaos
Mario Tennis Aces
Mostly deterministic ball physics
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Kick Off 2
Set plays and formation knowledge sit underneath
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.