There is a distinct difference between a MIL that butts in when she has no business doing so and a MIL that wants to have a part in her son's, DIL's, and grandkids' lives.
I will agree that she shouldn't force her will on the DIL or anyone's life, but you have to accept her in your life. Just as he should accept your parents in his.
There shouldn't be a dominant anyone in a family. Yes certain problems will take priority over others but that doesn't justify making problems just to get attention.
If his mother became handicapped or senile or whatever and she needed attention or some kind of financial help, would you be supportive or would you bust his balls and pull the her or me move?
I am not saying that the wife isn't important. She is very important. Some cases more important than the husband, but what I am saying is priorities are. If the kids need your time, you concentrate on the kids. If you or him need something then you concentrate on that. If one of the parents have a nissue, then worry about that. As long as the needs are legit why should either of you worry.
If you have issues with your MIL, then maybe you two should talk it out or at least you should try to be the better person and make a mends. There will always be issues with extended families, but you should have thought that one out before you got married.