head to head
Mario Sports Mix asks more than WWE 2K15, and the gap is variance.

Execution · Competitive PvP
Party sports where light timing and item luck outweigh deep strategy.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
Mario Sports Mix leans Execution (Competitive PvP); WWE 2K15 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.
Mario Sports Mix
Timing shots and blocks matters but stays party-game forgiving
WWE 2K15
Reversal timing windows decide most exchanges
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Sports Mix
Human opponents fake passes and shots in versus play
WWE 2K15
Human opponents bait reversals and vary move timing
Mario Sports Mix leans clearly harder on variance.
Mario Sports Mix
Item drops and special shots inject deliberate chaos
WWE 2K15
Chain-wrestling rock-paper-scissors minigames add randomness
WWE 2K15 leans a little harder on optimization, though the gap is small.
Mario Sports Mix
Shallow team and court knowledge caps quickly
WWE 2K15
Move sets, stamina and match pacing are learnable systems
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.