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

Reads · Grand Arena
A tactical breach-and-defend shooter driven by mind games over angles and gadgets.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Rainbow Six Siege leans Reads (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Rainbow Six Siege
Crisp aim required but TTK is unforgiving.
Warcraft III: Reign of Chaos
Micro of heroes and units decides fights
Rainbow Six Siege leans clearly harder on reads.
Rainbow Six Siege
Defenders adapt holds; attackers fake and bait.
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.
Rainbow Six Siege
Site rotations only; loadouts deterministic.
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Warcraft III: Reign of Chaos leans clearly harder on optimization.
Rainbow Six Siege
Operator picks, gadget placement, and utility usage.
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.