MC went back in time during training in space-time black hole like thing. Ended up in the distant past and taught humans the best ways of alchemy and used formations to create powerhouses to free them from being slaves. When he went back to his timeline,he was called one of the something ancestors. It is an alchemy focused novel.
Found it actually. The name of the novel is Unrivaled Medicine God, probably one of the best alchemy wuxia. The alchemy doesn't become irrelevant after a few arcs and it is pretty well explained with its own Dao.
Thanks for posting the answer to your own question. I was watching this thread in hopes someone would answer as I've been looking for good alchemy/crafting novels, too.