eh, they just need to twist around the beginning of the story. like it's an ancient mecha that have been passed generational of bloodlines and something like that.
also, this come to my mind, my fav movie "Real Steel" about robot boxing, they used old robot they found, the rest is spoiler...
they should've just remove the isekai and "power score whatever" part, literally the series stand with it's own sci-fi mecha military world building, characters and conflict between groups.