head to head
Neither is simply harder - they are hard in different places. Marvel vs. Capcom 2: New Age of Heroes demands more execution; Warcraft III: Reign of Chaos demands more variance.

Execution · Grand Arena
Chaotic tag fighter whose top tiers reward blistering execution and assist mastery.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Marvel vs. Capcom 2: New Age of Heroes leans Execution (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Marvel vs. Capcom 2: New Age of Heroes leans clearly harder on execution.
Marvel vs. Capcom 2: New Age of Heroes
infinite combos and assist timing demand elite hands
Warcraft III: Reign of Chaos
Micro of heroes and units decides fights
Marvel vs. Capcom 2: New Age of Heroes leans a little harder on reads, though the gap is small.
Marvel vs. Capcom 2: New Age of Heroes
humans bait assists and mix high-low constantly
Warcraft III: Reign of Chaos
Scouting and out-guessing a human opponent's tech
Warcraft III: Reign of Chaos leans clearly harder on variance.
Marvel vs. Capcom 2: New Age of Heroes
fully deterministic engine
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Warcraft III: Reign of Chaos leans clearly harder on optimization.
Marvel vs. Capcom 2: New Age of Heroes
team order, assist synergy, and matchup knowledge
Warcraft III: Reign of Chaos
Build orders, creeping routes, and matchup theory run deep
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.