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
Arcade baseball testing hit timing and pitch prediction in versus play.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
Mario Superstar Baseball 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 Superstar Baseball
Bat timing and charged pitches are the core motor test
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 Superstar Baseball
Guessing a human pitcher's mix is the versus layer
WWE 2K15
Human opponents bait reversals and vary move timing
Mario Superstar Baseball leans a little harder on variance, though the gap is small.
Mario Superstar Baseball
Star swings and bobbles add bounded randomness
WWE 2K15
Chain-wrestling rock-paper-scissors minigames add randomness
WWE 2K15 leans a little harder on optimization, though the gap is small.
Mario Superstar Baseball
Chemistry pairings and lineups are quickly learned
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.