Mics pick up too much leakage from the drums and guitars.
Buddy, you need to tell your drummer and guitar player to take their instruments to the doctor!
My dad played his '66 B-15 in several different types of bands using stage volume, mics, and with PA support for 40 years and never had a problem.....I continue to use the same amp to this day. It's my personal opinion that if you're cranking 400 watts and that's not enough:
A) you're either deaf, B) the rest of your band is too damn loud, C) all of the above.
It's all about personal preference....an age old argument that we could spend 200 pages on this thread on. Whatever floats your boat man, I hope there was no harm done w/ my little jab....I prefer to relish the possibility of a true-to-God reissue of my favorite amp of all time!!!
Cheers

Then when they say I'm too loud, I ask the guitarists to turn down.