Some degree of respect should be given to veteran group members as well. If the bassist thinks his sound is great and the guitarist thinks it sucks, who is right? The answer may be neither because tone is subjective. The OP suggests the bassist, audio tech, and rest of the band think the tone of the bass is fine. Why do you think the guitar player is the only one who has a clue.
I think the guitar player should get some say. However getting a sound on stage should be a negotiation between all members. If guitar ask for the bassist to bump the low end, reasonable concession can be given. However, consideration should be given to how the change impacts other band members and how it impacts house sound. If there is a disagreements, the group leader normally gets the final say. I would suggest the group leader consult with the audio tech on this particular matter, as having massive lows bleeding of the stage is a pretty reliable recipe for bad house sound.
If the guitar player is being judgy and acting like his opinion carries more weight than the everyone else, he probably needs to be checked. Of course, one might consider how rare and valuable the guitarist's skillset is. Sometimes the situation warrants giving someone who can who really bring "it" a bit more latitude, regardless of whether they or correct or being rationale. Sometimes the price of dealing with super talented artists is accepting a narcissistic attitude and offensive behavior. I don't necessarily like it, but it is sometimes a valid choice IME.