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.

Optimization · Grand Arena
Large-scale RTS testing economic optimization, multitask speed and prediction of human build choices.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Supreme Commander 2 leans Optimization (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Warcraft III: Reign of Chaos leans a little harder on execution, though the gap is small.
Supreme Commander 2
Macro APM across huge armies separates skirmish winners
Warcraft III: Reign of Chaos
Micro of heroes and units decides fights
Warcraft III: Reign of Chaos leans a little harder on reads, though the gap is small.
Supreme Commander 2
Multiplayer rewards scouting and predicting a human's tech switches
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.
Supreme Commander 2
Open maps leave little hidden beyond fog of war
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Supreme Commander 2
Economy ratios, build orders and research routing are deeply 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.