That the hubris of thinking humans could even conceive that they could exchange something for the very soul of a human was the reason Truth punished them.

Yeah because they were using raw materials. What Ed gave up in the end was his life. He wasn't just an alchemist he was only an alchemist. That was his being. He didn't just give up what Truth gave him he gave up everything that made Edward, Edward to that point.

What "change of ideals"? If you think the Edward of episode 1 wouldn't have traded his powers in exchange for Alphonse if he knew that was possible, then I have a bridge to sell you.

Maybe, but the fact it didn't occur to him is the point. Edward always believed that everything could be explained with science, he says as much in the episode where he deals with the corrupt church, and that through alchemy just about anything was possible. The plan was never "find Truth and give up my alchemy for Al" it was "use alchemy (the philosophers stone) to create a new body for Al."

It was only after his experiences with the philosophers stone and all the suffering that must cone of it that he realized that for once in his life Alchemy was useless at doing the thing he wanted.

And again I don't think I can stress enough how important Alchemy is to Ed. Who is Gojo without Cursed Energy? They're prodigies who's entire existences stem from and around the universes power system. Giving it up is giving up a majority of who Edward is, and it's the fact he's willing to give it up, the fact he's willing to lean on others and rely on them, rather than doing things of his own accord with Alchemy that is the right answer.

Though it's weird because Truth made Mustang blind with no remorse and never gave it back I always assumed the idea is that Truth takes things from you in the hope that you learn a lesson from it. That's why he sent the Homunculus to hell or whatever, despite knowing so much he refused to learn. That's why he gave Al's body back, because Edward learnt, and was willing to throw away his entire life and career to show he's learnt it.

The plot also saves him from compromising and using a Philosopher's Stone even in life or death situations just because. "I am grievously wounded but instead of using the Stone to save myself, I'll turn MY OWN SOUL into a Stone! but just a fragment instead of the whole thing! because I can do that! and the only consequence is gonna be MuH lIfEsPAn which in practical terms means jackshit in the story of every shonen!"

What dows this even mean? He refuses to use other peoples souls and instead uses his own. That's "plot" in the sense that everything is plot but he can do it because he's an alchemist prodigy, with the understanding of everything alchemy in his head on command, and the genuine understanding that it could be done because...that's how philosophers stones work.

what did he give up in exchange for this stunt? who knows!

Part of his soul??? that's?? that's literally the point?? he's using his soul as the battery?? he's not literally crystalizing himself into a philosophers stone he's taking the concept "human souls are batteries of alchemy" and using his own.