head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Practiced Mastery
Combo execution through scripted Outworld brawls, alone or in co-op.

Execution · Practiced Mastery
A musou-style hack-and-slash letting players mow down hordes as One Piece characters.
Mortal Kombat: Shaolin Monks leans Execution (Practiced Mastery); One Piece: Pirate Warriors 4 leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Shaolin Monks
Combo juggling and launcher timing carry combat
One Piece: Pirate Warriors 4
crowd-clearing combo execution against hordes
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Shaolin Monks
Bosses telegraph fixed Outworld patterns
One Piece: Pirate Warriors 4
enemies are scripted mobs, not adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Shaolin Monks
Encounters repeat identically once learned
One Piece: Pirate Warriors 4
minimal randomness in stage encounters
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat: Shaolin Monks
Move unlocks, co-op synergies and boss patterns reward study
One Piece: Pirate Warriors 4
character builds and combo routing are learnable
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.