Therefore, at best, the movie I, Robot is not a prequel to Asimov's series, but rather it sets up a completely divergent universe, "inspired" by his works.
So? How is that in any way a bad thing? Blade Runner
is radically different from its source, and it's one of the finest SF movies ever made.
It is a mistake to assume that the point of an adaptation is to copy the original. That would be a waste of time and effort. The point of an adaptation is to adapt
-- to take an idea that exists in one form and transform it into something new and different.
It should be taken as read that a movie based on a book series -- or particularly one based on an anthology, something it would be impossible to translate exactly -- is going to change things and create something different from the source. That's nothing to complain about in and of itself. If the new story manages to get across the core elements and ideas of the original, then that is what matters, regardless of how different the details are. After all, this is fiction, not reality. None of it actually happened, so it's kind of pointless to harp on whether the details are accurate. Hell, even historical fiction is understood to have the right to take liberties with real events and people if it serves the story.