Dear Jazzyvee,
Please pardon me if I seem pushy, as I don't mean to, but I agree, that you might chat with the keyboardist and anyone else who has this problem with the sound, and setting up a band meeting outside the venue and your instruments, to present the assessment and opinions from the bartender (the hotline to the pub's manager and the owner) and the patrons, concerning the band's volume, sound distribution, and equalization issues, as I think you have indicated is your core concern.
Could the bandleader/guitarist invest in an attenuator, like the old Marshall Powerbrake, which may offer a way to try to maintain the driven guitar tone without providing scorched earth volumes? Alternatively, would a compressor help the bandleader/guitarist get their desired lead tone? Would it be prudent to suggest playing through a board and into a PA so that the sound check levels/sound and distribution can be manicured before, during, and after solos, excepting the drummer, and so the sound placed accurately (I totally get this may be a heck of a stretch as no PA may be conveniently available). While I don't know what else you've suggested, I assume you have offered a veritable treatise of alternatives of the status quo to the "Monster(s) of Rock!".
I also agree with your point about the importance of pub's patrons having raised about the sound issue(s) with you, and they are a key determinant in playing in the venue as they are the venue's key determinant. Might you recommend that making a change to the band's approach is necessary and founded, as the band will lose audience members or even venue access? If people just leave the band as a result of not finding a good solution to this hitch, then the task of the bandleader to find competent replacement musicians may also suffer due to word of mouth (I'm not implying those words are yours, but that they may be observers, or another leaving band member, or other people in the scene) due to the bandleader's organizational ethic and the guitarists' priorities regarding their sound and not serving the song.
Obviously, I am just parroting the points that you raised and perhaps extending them a bit, as I am only suggesting that your most logical argumentation may reach "Bando Calrissian", whose name and reputation is associated with this act, as is their bottom line, is offered objectively through fact, as the guitarists' views are not shared by audience members or the management hierarchy. And the only way to reach this individual or the other guitarist I truly believe is with a non-confrontational, but concrete and data-driven assessment of what factors are not working, while delivered by the rest of the band, not just you or you and the keyboardist (sussing out who feels as you do, but won't snitch, may be a concern). Objectivity may prevent most tantrums in this meeting, as it is the data, not you and the band per se, that disagrees with the situation and the bandleader's actions.
And if it fails, I agree with you: walk. There have to be other more savory live music performance opportunities, and better bands to join, that are available to you. Maybe start your own with the keyboardist. I dunno. Best of luck with it, and I am sorry you have to deal with this. I hate local politics. Cheers, and as always, please excuse any typos.
Best regards,
-Zut