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 · Pure Mechanics
High-speed arena shooter with twitch duels and warfare-scale vehicle modes.
Marvel vs. Capcom: Clash of Super Heroes leans Execution (Competitive PvP); Unreal Tournament III leans Execution (Pure Mechanics).
Unreal Tournament III 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
Unreal Tournament III
Hitscan precision, dodge timing, and vehicle handling rule fights
Marvel vs. Capcom: Clash of Super Heroes leans a little harder on reads, though the gap is small.
Marvel vs. Capcom: Clash of Super Heroes
Baiting a human's assist call or super is the duel
Unreal Tournament III
Human opponents vary routes and dueling habits
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
Unreal Tournament III
Open arenas with fully visible pickups and players
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
Unreal Tournament III
Weapon spawns and power-up timing reward map study
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.