Having been involved in an abusive relationship in which I was sexually assaulted, I strongly disagree with that line of thinking. I think "rape" is a very distinct act that needs to be set apart from all the shades of grey that are implied in the term "sexual assault"

This is already reflected in the law. There are different charges for different kinds of sexual assault. Just as there are different charges for different kinds of theft, etc.

In common conversation, I don't expect someone to use the exact technical legal term. Someone tells me they were robbed, I'm not going to nitpick over the exact kind of theft they were talking about. Same with rape, or assault, or any other crime.