Ryan,
Mixing a band is an entirely different animal from mixing a musical play as I believe you know.
The off-line editor is as useful to musical theater operator as the iPad app is to the live band operator. One is very useful before load-in, one is very useful after load in. That is the most distilled essence of the difference I can think of.
I also mix the occasional festival and one-off show so I also am familiar with your side of the art. Neither discipline is superior. Both are quite different but still fun. As long as we are getting paid all is well.
With a musical 98% of the work is done before opening night. In fact significant work is done weeks before equipment load in. I must put in 10 to 20 hours into a mix before I even hook up my 30 wireless mics and work with actors. We musical mixers also are recalling cues that are (at times) only seconds apart. I regularly have 170 scenes in one performance. My 170 scene memories usually get revised about 12 times before opening night. The big overall picture an editor would provide is a huge benefit here.
That is why some add their voice to the editor software request choir. Like mine for example. 
Respect.
John
