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

Optimization · Pure Optimization
Alternate-history RTS where economy management and build orders win wars.

Optimization · Pure Optimization
RTS where you splice animals into custom armies before battle begins.
Command & Conquer: Red Alert leans Optimization (Pure Optimization); Impossible Creatures leans Optimization (Pure Optimization).
Command & Conquer: Red Alert leans a little harder on execution, though the gap is small.
Command & Conquer: Red Alert
Micro and base management under time pressure
Impossible Creatures
Standard RTS micro and army control
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Command & Conquer: Red Alert
PvP skirmish rewards predicting enemy pushes
Impossible Creatures
Human opponents counter your creature picks
Command & Conquer: Red Alert leans a little harder on variance, though the gap is small.
Command & Conquer: Red Alert
Fog of war conceals army composition
Impossible Creatures
Scouting hidden enemy combinations
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Command & Conquer: Red Alert
Ore economy and build orders decide games
Impossible Creatures
Creature-combining army design is deeply 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.