This is not a value judgment about the narrative quality of SC canon but let's just consider that maybe part of the appeal of Supreme Commander's canon might be that in a straight fight the things that exist in Supreme Commander's universe could beat the combat forces of other science-fiction canon's very reliably.
Let's take Warhammer 40k vs Supreme Commander? Oh, the Tyranids are this scary devourer of worlds? Bah, give an ACU some time around some mass deposits and it will have soul rippers up that will mop up those crunchy bugs like it's nobody's business. Oh? That Imperial or Chaos titan might slow down a commander a bit but while an ACU under the right circumstances can knock up a Galactic Colossus in less than 30 minutes it takes the Imperium of Man decades to build a Titan, (assuming they haven't lost the blueprints).
Starcraft? Well, Battlecruisers seem to be very ambiguous in how much damage they can actually do but the amount of ASF a Seton's player can cook up in less than an hour has to just be able to tear it to pieces. A siege tank can't be any stronger than a Pillar tank and an Ultralisk might have at most as much hp as a brick but a brick is a ranged unit. And Terran Marines? Oh my, you have to figure that enough t1 rushes on enough planets and while all it costs an ACU is a few minutes of its time, it wipes out an entire generation of young men.
You can say it's comparing apples and oranges but why is that? I think it's just because Supreme Commander is the only sci-fi game canon to acknowledge the absurdity of thinking that with future technology that any sentient race would use anything but robots to fight and use anything besides nano-technology enhanced automation to produce all of its war material and throwing in a few brains onto the battlefield to manage the whole thing. Pretty much the only defense you can make for any other kind of universe is the notion of technological setbacks in the future, religious objections to robotics, or some kind of other advantage to using sentients such as psychic soldiers and such.
The one thing I can say is that if Supreme Commander had had more expansions (no, not gonna mention SC2) then it would have been fun for there to be an 'organic' race like the Tyranids which could have distinct bio advantages like all units automatically self-heal and stuff like that. Perhaps even a 'demon' race but that's getting way out there for what SC has represented.