head to head
Neither is simply harder - they are hard in different places. Rivals of Aether demands more reads; Warcraft III: Reign of Chaos demands more optimization.

Reads · Grand Arena
A shield-less platform fighter where the absence of defensive options forces constant aggressive reads against human opponents.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Rivals of Aether leans Reads (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Rivals of Aether leans a little harder on execution, though the gap is small.
Rivals of Aether
Wavedash movement and off-stage edgeguards require real physical precision
Warcraft III: Reign of Chaos
Micro of heroes and units decides fights
Rivals of Aether leans clearly harder on reads.
Rivals of Aether
No shields forces constant adaptive prediction against human opponents
Warcraft III: Reign of Chaos
Scouting and out-guessing a human opponent's tech
Warcraft III: Reign of Chaos leans a little harder on variance, though the gap is small.
Rivals of Aether
Stage hazards add minor variance
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Warcraft III: Reign of Chaos leans clearly harder on optimization.
Rivals of Aether
Elemental mechanic interactions and matchup routing reward study
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.