In recent years there have been semi-staged concert performances at the Proms of My Fair Lady, Kiss Me, Kate and Oklahoma!. The staging frequently left something to be desired. What can be stated, however, is that from a musical viewpoint these were all excellent - a first class orchestra and good singers for whom vocal delivery was more important than acting. It goes without saying that John Wilson was in charge.
I have seen a concert performance of
The Gondoliers and it fell flat, IMHO the problem was that the same contains several small parts who add greatly to the visual & spoken parts, in a concert version one simply hears voices singing a few lines here and then, by the time that the audience has worked out whom is singing, s/he has finished.
My Fair Lady which has few singing parts, may perhaps work in a concert version, but not something such as
Showboat I do see a big difference between an oratorio, and an opera, and to my mind a concert version is a modern version of the former.