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
Foundational ice hockey sim testing stick timing and exploiting goalie angles.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
NHL Hockey leans Execution (Practiced Mastery); WWE 2K15 leans Execution (Competitive PvP).
NHL Hockey leans a little harder on execution, though the gap is small.
NHL Hockey
Skating angles, pass timing and shot placement decide goals
WWE 2K15
Reversal timing windows decide most exchanges
WWE 2K15 leans a little harder on reads, though the gap is small.
NHL Hockey
Against a human, baiting checks and goalie reads matter
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.
NHL Hockey
Puck bounces add light physical randomness
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.
NHL Hockey
Exploitable AI angles and line strategy are mappable
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.