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
A platform of millions of user-created multiplayer games spanning every genre, played mostly by younger audiences.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
Roblox leans Execution (Practiced Mastery); WWE 2K15 leans Execution (Competitive PvP).
WWE 2K15 leans a little harder on execution, though the gap is small.
Roblox
Many popular experiences are obby/PvP tests of hands
WWE 2K15
Reversal timing windows decide most exchanges
WWE 2K15 leans a little harder on reads, though the gap is small.
Roblox
Multiplayer experiences pit you against other kids' minds
WWE 2K15
Human opponents bait reversals and vary move timing
Roblox leans a little harder on variance, though the gap is small.
Roblox
User-generated content means constant unknown systems
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.
Roblox
Grind economies and trading reward system mastery
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.