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
Arcade tennis with timing-based PvP mind games.

Execution · Competitive PvP
AKI-engine N64 wrestler that perfected the grapple system later refined in No Mercy.
Mario Tennis Aces leans Execution (Competitive PvP); WCW/nWo Revenge leans Execution (Competitive PvP).
Mario Tennis Aces leans a little harder on execution, though the gap is small.
Mario Tennis Aces
Shot timing, charge mechanics, footwork
WCW/nWo Revenge
AKI grapple timing and reversal windows
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Tennis Aces
Online tennis demands reading opponent placement
WCW/nWo Revenge
Human opponents turn reversals into prediction duels
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Tennis Aces
Mostly deterministic ball physics
WCW/nWo Revenge
Slight randomness in momentum swings
WCW/nWo Revenge leans a little harder on optimization, though the gap is small.
Mario Tennis Aces
Character matchups and tech routes
WCW/nWo Revenge
Learning rosters' move sets and spirit flow converges
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.