I mean, that's quite possibly all true, and I'll agree knowing how we got to the ending we did, and what the intention was is interesting in a "how was the sausage made" way, but in the end what matters to me is the ending we actually have in the game that actually released.
(I'm not trying to give you a hard time or anything, to be clear- it is genuinely interesting the hints we have at what might have been planned based on what's in the game, but absent official clarification that seems unlikely, it's all pretty much speculation. Does make me wonder what on Earth enriched infernal iron was meant to be for if the engine was always meant to be unfixable, though)
Maybe we weren't originally meant to spend so much time with her, but in the release version, we do. Maybe the engine was planned from the beginning to be unfixable, but whether that was the original intent or not doesn't make the fact that there's a bunch of options that are at least plausible within the setting that you simply can't try- and there's not so much as a hand-wavey explanation for why you can't do any of the obvious stuff- less irritating. There's a reason so many people have the experience of seeing her ending for the first time and more or less responding with "Wait, what? Did I miss something somewhere?"
