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.

Execution · Competitive PvP
The toned-down crossover fighter matching Mortal Kombat's roster against DC superheroes.

Execution · Competitive PvP
The fourth Soulcalibur adds armor-breaking Soul Gauge pressure and Critical Finishes to its weapon dueling.
Mortal Kombat vs. DC Universe leans Execution (Competitive PvP); Soulcalibur IV 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.
Mortal Kombat vs. DC Universe
Juggle combos and klose kombat timing
Soulcalibur IV
Step-guard and just-guard timing keep a real physical ceiling.
Soulcalibur IV leans a little harder on reads, though the gap is small.
Mortal Kombat vs. DC Universe
Human mixups, though a simpler toolset than peers
Soulcalibur IV
Critical Finish threats add layers to adaptive mixup guessing.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat vs. DC Universe
Deterministic crossover combat
Soulcalibur IV
Soul Gauge is visible; no hidden info.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mortal Kombat vs. DC Universe
Mapping juggle routes and matchup tools rewards practice
Soulcalibur IV
Guard-crush pressure routes and frame data are studyable.
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.