But you touted the Interex as a positive example before the Imperium ruined everything in reply to someone saying the canon reforming Imperium was on the right track. When, in all actuality the Interex was a bit player that got eaten by the monstrous human faction rather than the monstrous fungus, or maggots, or whatever other horror.
Referencing the Interex as a positive sustainable example in any way seems head scratching.
No, here's what happened with the Interex: The Imperium comes about them and they are utterly puzzled about these fellas using way more advanced technology such as
actual AI and centaur-platforms that put them on par with Space Marines, then Erebus steals the Kinebrach Anathame and the Interex go fucking apeshit and they need to evacuate Horus off the planet like a little bitch because they're actually incapable of beating them. Then we lack all data for a while and we're told that they were destroyed in an Imperial campaign as precedent to the war against the Auretian Technocracy. Your nice claim about being stomped by a legion or two is validated nowhere, and you're free to go check
False Gods to verify.
Furthermore, this argument is dumb. This is going "the Interex don't work as well as the Imperium because they're not hypermilitarized all the time at all times and have 18
Übermenschen-Primarchs, 1 God-Emperor and vast other advantages dispersed across the Imperium by either vagaries of fate or random chance." We can
see that the Interex are more than capable of going toe to toe with Space Marines, we can
see that they're more than capable of scaring even the battle-hardened Luna Wolves who completely fail to put up an effective fight against them and we can
see that the Interex were more than willing to cooperate peacefully with aliens. What we
can't see is any evidence for your quaint claim that a single Legion beat them. The Interex spent their effort on other things than being as space macho as possible, and were most likely hampered primarily by simply not posssessing the large, vast population of the Imperium that could be marshalled at a moment's notice, while the Imperium was midway through a period of heavy expansion.
Did the Interex work out? No, not the least. The Imperium did destroy them in the end, but I never said it was perfect. But here's a secret, a deal, a trick of the trade if you will: Just because it failed then, there is no reason it will fail again when applied to different circumstances and situations, and the Interex did certainly seem to work rather fine until then. As far as things go, I can't say I'm terribly convinced by the argument that the incredibly anti-chaos-specced polity got fucked up by a non-chaos-worshipping hypermilitarized polity was its own fault or a proof that it could not work out. That's just a proof that the Imperium was more militarized, which we all knew it was in the first place. Especially when we don't actually know that much about the war with the Interex in the first place beyond empty conjecture.