head to head
Warcraft III: Reign of Chaos asks more than Arma 3, and the gap is optimization.

Execution · Grand Arena
Open military simulator and PvP sandbox.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Arma 3 leans Execution (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Arma 3 leans a little harder on execution, though the gap is small.
Arma 3
Bullet drop, stance, sway, weight all matter
Warcraft III: Reign of Chaos
Micro of heroes and units decides fights
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Arma 3
PvP and milsim ops reward prediction
Warcraft III: Reign of Chaos
Scouting and out-guessing a human opponent's tech
Arma 3 leans a little harder on variance, though the gap is small.
Arma 3
Mission scripts and AI behavior vary
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Warcraft III: Reign of Chaos leans clearly harder on optimization.
Arma 3
Loadout planning and tactics solvable
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.