head to head
Neither is simply harder - they are hard in different places. StarCraft II: Wings of Liberty demands more execution; Warhammer 40,000: Dawn of War II demands more variance.

Execution · Grand Arena
Real-time strategy where hands, reads, and build optimization all matter at the top.

Execution · Grand Arena
Hero-driven squad RTS where wargear optimization and ability timing combine with reading aggressive opponents.
StarCraft II: Wings of Liberty leans Execution (Grand Arena); Warhammer 40,000: Dawn of War II leans Execution (Grand Arena).
StarCraft II: Wings of Liberty leans clearly harder on execution.
StarCraft II: Wings of Liberty
APM, macro, micro-control under pressure
Warhammer 40,000: Dawn of War II
Hero ability activation and squad retreat timing are mechanically demanding
StarCraft II: Wings of Liberty leans a little harder on reads, though the gap is small.
StarCraft II: Wings of Liberty
1v1 ladder vs adaptive humans modeling you
Warhammer 40,000: Dawn of War II
Opponent army composition and hero focus must be predicted
Warhammer 40,000: Dawn of War II leans clearly harder on variance.
StarCraft II: Wings of Liberty
map spawns minor; mostly known
Warhammer 40,000: Dawn of War II
Retreat damage, wargear drops, and map control variance add uncertainty
StarCraft II: Wings of Liberty leans clearly harder on optimization.
StarCraft II: Wings of Liberty
build orders, economy curves heavily solved
Warhammer 40,000: Dawn of War II
Wargear builds and ability upgrade sequences are optimizable
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.