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
Substitution baiting against humans atop simple anime-fighter inputs and team picks.

Execution · Competitive PvP
Reversal timing and pacing against an opponent baiting your counters.
Naruto Shippuden: Ultimate Ninja Storm 2 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.
Naruto Shippuden: Ultimate Ninja Storm 2
Timing substitutions and combos matters but inputs are simple
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.
Naruto Shippuden: Ultimate Ninja Storm 2
Versus humans, baiting substitutions is the real layer
WWE 2K15
Human opponents bait reversals and vary move timing
WWE 2K15 leans a little harder on variance, though the gap is small.
Naruto Shippuden: Ultimate Ninja Storm 2
Nothing hidden once both characters are known
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.
Naruto Shippuden: Ultimate Ninja Storm 2
Team composition and chakra management have solvable lines
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.