head to head
Neither is simply harder - they are hard in different places. Company of Heroes demands more variance; StarCraft demands more optimization.

Execution · Grand Arena
WWII squad-tactics RTS where cover micro, sector pressure, and doctrine counters form an interlocking test.

Optimization · Grand Arena
A real-time strategy classic where perfected build orders and mechanical speed decide most matches.
Company of Heroes leans Execution (Grand Arena); StarCraft 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.
Company of Heroes
Infantry cover micro and suppression-break timing are precise demands
StarCraft
APM and micro control ceiling is huge
Company of Heroes leans a little harder on reads, though the gap is small.
Company of Heroes
Opponent sector pushes and doctrine choices must be predicted
StarCraft
scouting and predicting human opponent builds
Company of Heroes leans clearly harder on variance.
Company of Heroes
Reinforcement point capture variance and munitions drops add uncertainty
StarCraft
minimal hidden info beyond fog of war
StarCraft leans clearly harder on optimization.
Company of Heroes
Resource point priority and doctrine selection are learnable systems
StarCraft
build orders and economy are near-solvable
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.