head to head
Neither is simply harder - they are hard in different places. Capcom vs. SNK 2: Mark of the Millennium 2001 demands more execution; Warcraft III: Reign of Chaos demands more variance.

Execution · Grand Arena
Crossover fighting game where groove systems and footsies meet deep execution demands.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Capcom vs. SNK 2: Mark of the Millennium 2001 leans Execution (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Capcom vs. SNK 2: Mark of the Millennium 2001 leans clearly harder on execution.
Capcom vs. SNK 2: Mark of the Millennium 2001
Strict links, roll cancels, groove mechanics
Warcraft III: Reign of Chaos
Micro of heroes and units decides fights
Capcom vs. SNK 2: Mark of the Millennium 2001 leans a little harder on reads, though the gap is small.
Capcom vs. SNK 2: Mark of the Millennium 2001
Footsies and conditioning against adapting humans
Warcraft III: Reign of Chaos
Scouting and out-guessing a human opponent's tech
Warcraft III: Reign of Chaos leans clearly harder on variance.
Capcom vs. SNK 2: Mark of the Millennium 2001
Almost no randomness in matches
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Warcraft III: Reign of Chaos leans clearly harder on optimization.
Capcom vs. SNK 2: Mark of the Millennium 2001
Groove selection, team order, matchup theory
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.
full breakdown
Capcom vs. SNK 2: Mark of the Millennium 2001 →
full breakdown
Warcraft III: Reign of Chaos →