1. Lin might also know that it's not true by that standard.
2. Those problems have been curtailed for now and in the Trust. The Imperium didn't start out a galaxy wide oppressive asshole tyranny either. We have thousands of years in which to fall to asshattery.
3. Much of your argument was predicated on him being strong enough to defeat them, which I see as incredibly unlikely.
4. He wasn't always barely kept alive. Chaos defeating him at the pinnacle of his power was how he was crippled in the first place. Also I don't think it likely he was "ultimately a man" in the first place given he was a gestalt fusion of many shamans throughout history.
Not really getting into the over all argument, but
1. So far Lin's knowledge has been entirely accurate. Until he's been proved wrong if he says nah I'm fine with it for now.
2. Nah the Imperium was always asshatty. The sheer level of egregious oppression was slightly lower around the GC, but it was still egregious and oppressive.
3. Well it doesn't look like there is a way for anyone or anything that isn't named Mag'ladroth or Gork and Mork to beat Chaos 1vs1 and if they were to go for each other...well I don't think there'd be much of a galaxy left after that. Optimistically Emp's return probably doesn't mean chaos punch face, but some other means of dealing with them.
4. He also wasn't always being sacrificed 10,000 psykers everyday or having the combined worship of the galaxy spanning imperium focused on him. As for chaos defeating him...eh see below. Though at the end of the day emp's humanity (and lack there of) is what got him gibbed in the end.
I've always been of the opinion that the 'feat' of Horus-backed-by-Chaos essentially one-shotting Emps isn't really a good indicator of his strength, since a) he was holding back because of the whole 'I actually care if my favorite son dies.' thing Sanguinis getting offed triggered, b) he was doing a bunch of other stuff like keeping the planet from falling into the Warp, which means he wasn't exactly operating at 100% to begin with, and c) even if you don't think the above two points are valid, he put Horus into essentially the same state Horus put him in the second he actually started attacking, and then obliterated his soul so thoroughly even Chaos couldn't un-kill him. So, if nothing else, I think having Emps as an allied god will be a major advantage.
Eh it kind of is, though to explain.
Basically the fact that instead of confronting Emps himself and instead worked through a proxy like Horus basically says that regardless of the fact that he was significantly weaker than them his strength was enough to cause them real harm if they went for him directly.
Even then as you said that the second he decided to go all out he was able to bring down Horus nearly instantly, despite the fact that Chaos had infused themselves into him despite being mortally wounded and at the same time powering the astronomicon and (critically) keeping the Dragon asleep.
So what you guys arguing about worshipping a new god that's cool. I say the trust should worship someone who cares about you and tries to deal with those spiders.
Worship Mother Isha
Humans who worshipped the emperor in the days of the Imperium didn't have faith. They had actual knowledge that he existed and enabled their existence by the Astronomican if nothing else. With him dying the vast majority of humans that worshipped him ceased to do so, likely because it wasn't faith in the first place. It was an exchange of worship for divine power.
Nah not really.
Take the Dragon's nest that continue to worship emps despite acknowledging that he was dead.
The faith in the Emperor was just that real faith. Most of the unwashed masses of humanity didn't know what the Astronomicon was, that's just words to them. Almost all would live and die short, unhappy painful lives painfully bound to the planet, but they had faith in a man sacrificing himself upon a golden throne in the same way a peasant in medieval europe dutifully comes to church every sunday to worship a man who died on the cross, because they truly believe that he could save them regardless of proof, or lack there of and that has continued even after his death.
It wasn't just a transaction of faith, it was a real faith. Too real in fact as it turned to zealotry.
That was defeating a Chaos Champion, not a Chaos God. Those are very very different things.
Horus is weird.
In canon he goes to Moltarch and receives the same power as emps, in this quest as I understand each chaos god infuses part of themselves into him on a fundamental level to give him the strength needed.
Either way chaos gives him a vast amount of power and when Emps is brought to the state they want and finally retaliates they abandon Horus shortly after.
