I dont get why they need to do EA: Larian could easily do normal game release.
I think it should be fun if CDPR published this as their first non-own-game publish. Ive been gamer since the 90s, and trust me when when i say this thatt they know everything what happens inside game industry. Its probably mods who carry messages.
Simple: Experience. They did EA for both previous original sin games and the EA period made those games much better than they were in EA. And if Swen is honest about his claims (which I personally have no doubt), BG3 will be much bigger in scale. And he keeps using the word "permutations" which is a very appropriate term when it comes to projects this big. I write simple programs for my engineering projects and even tho they are fairly simple, I always come up something weird/unexpected after a while. And since permutations scale up exponentially with the number of components, they have millions untested possibilities in their hands. EA will be that period, thousands of players testing the game and speeding up the polishing stage.
I have no idea what you mean by "non-own-game". If you mean what I think you mean, I see absolutely no reason for CDPR to publish a game when they have GOG.