head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.

Execution · Competitive PvP
Reversal-timing wrestling that becomes a prediction game against humans.
WWE 2K15 leans Execution (Competitive PvP); WWE SmackDown! Shut Your Mouth 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.
WWE 2K15
Reversal timing windows decide most exchanges
WWE SmackDown! Shut Your Mouth
Grapple timing and reversals reward quick hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
WWE 2K15
Human opponents bait reversals and vary move timing
WWE SmackDown! Shut Your Mouth
Versus friends, reversal baiting becomes a prediction game
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
WWE 2K15
Chain-wrestling rock-paper-scissors minigames add randomness
WWE SmackDown! Shut Your Mouth
Mild AI and momentum randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
WWE 2K15
Move sets, stamina and match pacing are learnable systems
WWE SmackDown! Shut Your Mouth
Move-set knowledge and momentum management are learnable
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.