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.

Reads · Grand Arena
Cold-War base-builder where tight production queues and superweapon races define competitive play.

Optimization · Grand Arena
Large-scale RTS testing economic optimization, multitask speed and prediction of human build choices.
Command & Conquer: Red Alert 2 leans Reads (Grand Arena); Supreme Commander 2 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.
Command & Conquer: Red Alert 2
Superweapon timing and unit grouping require practiced multitasking
Supreme Commander 2
Macro APM across huge armies separates skirmish winners
Command & Conquer: Red Alert 2 leans a little harder on reads, though the gap is small.
Command & Conquer: Red Alert 2
Opponent faction and rush timing must be scouted and predicted
Supreme Commander 2
Multiplayer rewards scouting and predicting a human's tech switches
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Command & Conquer: Red Alert 2
Map layout is fixed; very little hidden RNG in unit behavior
Supreme Commander 2
Open maps leave little hidden beyond fog of war
Supreme Commander 2 leans a little harder on optimization, though the gap is small.
Command & Conquer: Red Alert 2
Build queues and power grid management are highly optimizable
Supreme Commander 2
Economy ratios, build orders and research routing are 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.