IMHO: Kaye could SING it. Kahn could sing AND act it.
I saw a production at REPRISE in L.A. many years ago and thought Mimi Hines was much more entertaining than Imogene Coca.
Kahn had a tough time of it. She was also fired from the movie of MAME. There are the rumors about both firings, but I don't think it appropriate to post rumors.