head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Optimization · Pure Optimization
A real-time strategy game where mastering build orders and economy management decides most matches.

Optimization · Pure Optimization
Alternate-history RTS where economy management and build orders win wars.
Age of Empires II: HD Edition leans Optimization (Pure Optimization); Command & Conquer: Red Alert leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Age of Empires II: HD Edition
click speed and micro help but secondary
Command & Conquer: Red Alert
Micro and base management under time pressure
Command & Conquer: Red Alert leans a little harder on reads, though the gap is small.
Age of Empires II: HD Edition
predicting human opponent strategy and timing
Command & Conquer: Red Alert
PvP skirmish rewards predicting enemy pushes
Command & Conquer: Red Alert leans a little harder on variance, though the gap is small.
Age of Empires II: HD Edition
minor map and resource randomness
Command & Conquer: Red Alert
Fog of war conceals army composition
Age of Empires II: HD Edition leans a little harder on optimization, though the gap is small.
Age of Empires II: HD Edition
build orders and economy are near-solvable
Command & Conquer: Red Alert
Ore economy and build orders decide games
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.