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

Execution · Competitive PvP
Party baseball testing swing timing and pitch-guessing against friends under item chaos.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
Mario Super Sluggers 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 Super Sluggers
Swing timing and fielding reactions decide most plays
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 Super Sluggers
Pitcher-batter guessing games against humans reward prediction
WWE 2K15
Human opponents bait reversals and vary move timing
Mario Super Sluggers leans clearly harder on variance.
Mario Super Sluggers
Star powers and item errors inject party 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 Super Sluggers
Team chemistry and lineup building are shallow but real
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.