head to head
Neither is simply harder - they are hard in different places. Call of Duty: Warzone demands more execution; Warcraft III: Reign of Chaos demands more optimization.

Execution · Grand Arena
Battle royale built on COD's tight gunplay.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Call of Duty: Warzone leans Execution (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Call of Duty: Warzone leans clearly harder on execution.
Call of Duty: Warzone
Long-range gunfights reward perfect aim
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.
Call of Duty: Warzone
Rotations and third-party reads decide fights
Warcraft III: Reign of Chaos
Scouting and out-guessing a human opponent's tech
Call of Duty: Warzone leans clearly harder on variance.
Call of Duty: Warzone
Drops, loot, circles inject real RNG
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Warcraft III: Reign of Chaos leans clearly harder on optimization.
Call of Duty: Warzone
Meta loadouts and rotations heavily solved
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.