The Ramban defended the Rambam personally, not the Shitos. He argues on the Shitos. The Ritva, in Sefer Zichronos, defended the Shitos as well, but goes on to add that he doesn’t agree with them, but they aren’t nonsense.
In fact, very few and far between were those who took on the complete approach of the Moreh. It is a recent thing to accept it as the main view, since it appeals more to western thinking.
Being that it is a reborn Hashkafa and doesn’t come with a long chain behind it, many parts are interpreted freshly that are hardly what the Rambam had in mind. An example is the Bilaam donkey thing. I hear people lovingly quoting that passing statement while imagining what “they” would say if I would have said that, and ignoring the open statements of the Rambam describing the speaking donkey as a Ness carried out by a Malach and being prepared Erev Shabbos Bein Hashmashos.