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
A multiplayer survival sandbox where human adversaries make every base a target.

Optimization · Grand Arena
Large-scale RTS testing economic optimization, multitask speed and prediction of human build choices.
Rust 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.
Rust
Aim and recoil control crucial in PvP encounters.
Supreme Commander 2
Macro APM across huge armies separates skirmish winners
Rust leans a little harder on reads, though the gap is small.
Rust
Human raiders and roamers adapt to your patterns constantly.
Supreme Commander 2
Multiplayer rewards scouting and predicting a human's tech switches
Rust leans a little harder on variance, though the gap is small.
Rust
Loot and resource spawns add modest randomness.
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.
Rust
Base design, farming, and raid prep dominate strategy.
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.