This issue is is very relative to the types of gigs and audiences you play to. I think OMB performers can replace bands in certain venues. At others I don't think they can.

I play with a classic rock band to audiences between 25-45. I just can't see a a OMB playing Van Halen, Led Zepplin or Red Hot Chilli Peppers anywhere close to a live rock band.

On the other hand we play some gigs where we are followed by a DJ serving up hiphop to an audience 25 and under. Then we are really out of the picture. The hiphop DJ can pull in a bigger audience at those venues than we do. So it all depends on the type of audience you are playing to.