I can't really make an informed comparison here. I've never really given Madonna a hard listen. She has made great dance music fluff, if you know what a fluffer is.
It seems she has made a daring album at a critical point in her career, and if one thinks Bruce has as well (I don't!) then maybe you see a basis for a comparison.
Both artists are populists of different styles who reached the peak of their fame sometime around 1984.
That's about the only common ground I see.
Bruce is one of the greatest songwriters in the history of recorded music.
Madonna is the grandmother of slut - pop.
When an artist has to dress up in fake garb (from exposed bras to bogus eye patches), or undress in order to sell their music, I lose interest quick.
Let's talk about Roseanne Cash or Lucinda Williams, maybe.
I've never given a rat's ass about popularity. I don't care about what others like. But I want to hear a good song.