IME, blending backline is easier when you only have the vocals in the PA, because you're not guessing what's happening with instrument levels and eq in the FOH.
Plenty of old school club and bar bands did this by knowing how to build arrangements and slot tones, trusting each other to support the vocals, and simply listening to one another.
Plenty of old school club and bar bands did this by knowing how to build arrangements and slot tones, trusting each other to support the vocals, and simply listening to one another.