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 · Practiced Mastery
Timing-based grapple execution with light opponent prediction in multiplayer matches.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
WCW Mayhem leans Execution (Practiced Mastery); WWE 2K15 leans Execution (Competitive PvP).
WCW Mayhem leans a little harder on execution, though the gap is small.
WCW Mayhem
Timing grapples, reversals and strikes decides every match
WWE 2K15
Reversal timing windows decide most exchanges
WWE 2K15 leans a little harder on reads, though the gap is small.
WCW Mayhem
Human opponents in versus add a modest prediction layer
WWE 2K15
Human opponents bait reversals and vary move timing
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
WCW Mayhem
Weapon spawns and AI behaviour add minor noise
WWE 2K15
Chain-wrestling rock-paper-scissors minigames add randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
WCW Mayhem
Learning move lists and match-type quirks is a fixed problem
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.