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 · Competitive PvP
An anime fighter testing combo execution and counter-baiting against human opponents.

Execution · Competitive PvP
The toned-down crossover fighter matching Mortal Kombat's roster against DC superheroes.
Dragon Ball Z: Budokai 3 leans Execution (Competitive PvP); Mortal Kombat vs. DC Universe leans Execution (Competitive PvP).
Mortal Kombat vs. DC Universe leans a little harder on execution, though the gap is small.
Dragon Ball Z: Budokai 3
Combo execution, teleport counters and beam timing demand hands
Mortal Kombat vs. DC Universe
Juggle combos and klose kombat timing
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Dragon Ball Z: Budokai 3
Versus humans, baiting teleports and guessing cancels decides exchanges
Mortal Kombat vs. DC Universe
Human mixups, though a simpler toolset than peers
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Dragon Ball Z: Budokai 3
Almost nothing random beyond minor clash inputs
Mortal Kombat vs. DC Universe
Deterministic crossover combat
Mortal Kombat vs. DC Universe leans a little harder on optimization, though the gap is small.
Dragon Ball Z: Budokai 3
Capsule builds and matchup knowledge underpin competitive play
Mortal Kombat vs. DC Universe
Mapping juggle routes and matchup tools rewards practice
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.