The first guardians (warlords) were probably the most evil.

Nah. They weren't twisted by the hive, drained the light of guardians, and is remembered in disgust

I wouldn't say a cult. That has a more of a... conforming, side to it. More like they embraced simply what Yor embraced, but to a lesser extent. They were still guardians, but they were clearly also affected by the Thorn. Kind of like how people might follow a celebrity a little too seriously. Dredgen being that celebrity of sorts. These guardians, Orsa and Teben, are never spoken of actually doing anything 'bad' or illegal or evil. Just that they... changed. Then again, I'm certain the whole story isn't revealed so we can speculate on that specific point.

Yeah but in the real world, sometimes a cult made after a celebrity tend to do evil things behind closed doors and not in public. In this scenario, the public being all guardians

Which may be true. I'll grant you that.

I always thought those cards were references to everyone using thorn back then, but now it's a lot scarier

Well, it is and it isn't. There are several cards specifically made to pay homage to the player base and the silliness that we do. In the Owl Sector Crisis, one of the dialogue sections was a person commenting on how guardians were 'fried in the head with light' because guardians would just dance, at random, with no music whatsoever. It's funny when you can tell the cards or dialogue is talking about us. Another Cabal report shows a Cabal strike team that fails and the acrobatics/dancing guardians ensued afterwards. So, you are right. It does hint at the Thorn era. But it also tries to explain, in a more serous sense, why it might have happened. -- Oh, my favorite one is the Shores of Time card. Where the person comments how if people would just hold B and C they would win, but dumb guardians go for A and lose the match.

Yeah that's Bungies sneaky way of insulting the players. Since no one checks the grimoire I'm not even mad. I laugh my ass off when I read those XD