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
High-speed tag-team execution and human prediction in gleeful early-Versus chaos.

Execution · Competitive PvP
The fourth Soulcalibur adds armor-breaking Soul Gauge pressure and Critical Finishes to its weapon dueling.
Marvel vs. Capcom: Clash of Super Heroes leans Execution (Competitive PvP); Soulcalibur IV leans Execution (Competitive PvP).
Marvel vs. Capcom: Clash of Super Heroes leans a little harder on execution, though the gap is small.
Marvel vs. Capcom: Clash of Super Heroes
Chain combos, assists and infinites demand fast precise hands
Soulcalibur IV
Step-guard and just-guard timing keep a real physical ceiling.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Marvel vs. Capcom: Clash of Super Heroes
Baiting a human's assist call or super is the duel
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.
Marvel vs. Capcom: Clash of Super Heroes
Hidden characters aside, everything is public
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.
Marvel vs. Capcom: Clash of Super Heroes
Team composition and infinite-combo knowledge define the meta
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.