Please can you supply these sources? AFAIK it's just two of the novels and the information in those are from what I would call questionable sources.
You're right, A Turner may know more. But he's not The Turner, he's a son (unconfirmed), and therefore may not have any special knowledge.
The quest class ship is just a nod to FFE and in ED lore doesn't mean anything, certainly not proof of anything (though I'd love it if they did introduce that into the narrative!)
No-one in game, including experts in the field of Zeno biology and Thargoids has ever mentioned factions or any names for them other than Thargoids. Even DB himself only ever calls them Thargoids.
Carl Linnaeus is hardly a questionable source. He has Thargoids working in his base and guarding it. These guard ships and their attack drones are vitnesed by several others.
This happened in 3275, I think. I see no reason why he should give the Thargoids a fake name.
All his info on the Klaxians are from the Oresrians. That is the weak link in the tale.
We have no first hand witnes reports on the Klaxians. When all we know of them is from what their enemy have told us, it should be taken with a pinch of salt.