head to head
Neither is simply harder - they are hard in different places. Age of Empires II: The Age of Kings demands more variance; StarCraft II: Wings of Liberty demands more execution.

Optimization · Grand Arena
The definitive medieval RTS where castle drops and farm economies decide empires.

Execution · Grand Arena
Real-time strategy where hands, reads, and build optimization all matter at the top.
Age of Empires II: The Age of Kings leans Optimization (Grand Arena); StarCraft II: Wings of Liberty leans Execution (Grand Arena).
StarCraft II: Wings of Liberty leans clearly harder on execution.
Age of Empires II: The Age of Kings
Micro, villager management, hotkey speed
StarCraft II: Wings of Liberty
APM, macro, micro-control under pressure
StarCraft II: Wings of Liberty leans a little harder on reads, though the gap is small.
Age of Empires II: The Age of Kings
High-level play is predicting human openings
StarCraft II: Wings of Liberty
1v1 ladder vs adaptive humans modeling you
Age of Empires II: The Age of Kings leans clearly harder on variance.
Age of Empires II: The Age of Kings
Fog, map gen, civ matchups
StarCraft II: Wings of Liberty
map spawns minor; mostly known
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Age of Empires II: The Age of Kings
Build orders refined over two decades
StarCraft II: Wings of Liberty
build orders, economy curves heavily solved
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.