I understand what you are saying but you are missing my point...the sound is still totally directional and compromised.
For any gig you need a PA. If the PA is that crap you can;t run Kick and snare as well as guitars ( bass is less of an issue as it carries way better) then you are going to sound crap anyway. Most PA's today are well enough equipped to handle multiple instruments well.
I have played many many gigs with no sound man and once the sound is set up, its pretty stable, especially if you have your relative sounds sorted ( cleans vs rhythm vs solo).
Most of my gigs I play are small pubs. Our PA is relatively simple and yet we put 2 guitars ( one is a Helix with no backline), bass and full drumkit, along with all vocals through it. Once set, you only have to make minor changes as the outputs are constant - one of the big advantages because you are not messing with volumes and mic placement.
You also miss about 80% of the benefit of the Kemper live IMO.
Just out of curiosity what PA do use to handle a full mix , i believe this might well be my 1st post 
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