head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Reads · Competitive PvP
Anime arena fighter where managing the substitution gauge is the real duel.

Execution · Competitive PvP
An anime arena fighter testing team-switch timing and counter prediction against humans.
Naruto Shippuden: Ultimate Ninja Storm 4 leans Reads (Competitive PvP); One Piece: Burning Blood 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 4
Simple inputs; movement and substitution timing matter
One Piece: Burning Blood
Combo timing and guard breaks need moderate hands
Naruto Shippuden: Ultimate Ninja Storm 4 leans a little harder on reads, though the gap is small.
Naruto Shippuden: Ultimate Ninja Storm 4
Versus humans, baiting substitutions is the core game
One Piece: Burning Blood
Human opponents bait switches and counters constantly
Naruto Shippuden: Ultimate Ninja Storm 4 leans a little harder on variance, though the gap is small.
Naruto Shippuden: Ultimate Ninja Storm 4
Minor support-assist chaos
One Piece: Burning Blood
Full-information arena with no hidden state
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 4
Team composition and matchup knowledge
One Piece: Burning Blood
Team composition and Devil Fruit matchups reward study
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.