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

Execution · Competitive PvP
Fast arena-fighter execution plus guessing games against a human opponent.

Execution · Competitive PvP
The toned-down crossover fighter matching Mortal Kombat's roster against DC superheroes.
Dragon Ball Z: Budokai Tenkaichi 3 leans Execution (Competitive PvP); Mortal Kombat vs. DC Universe 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.
Dragon Ball Z: Budokai Tenkaichi 3
Combo timing, dashes and beam clashes demand fast 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 Tenkaichi 3
Versus humans, baiting counters and vanish wars is prediction
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 Tenkaichi 3
Almost nothing hidden once both rosters are known
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 Tenkaichi 3
Character tiers and combo routes form a learnable layer
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.