I agree. He'd need a lot more character development than a 2 hour movie could give.Moon Knight would be a much better candidate for a TV show. The multiple identity issue would be hard to do justice to in a movie format compared to series.
Mental illness was handled pretty well in "Legion."I love Moon Knight.
I also think his "multiple personalities" make him a problematic candidate for modern mass-market media. We have such trouble with misrepresentation of mental health issues already, that this would probably not be a positive move for Marvel to make.