The very short answer to your question would be that sitting in different spots on stage, or even in the hall, will of course give you a different perspective of the ensemble's balance, and we adjust to that accordingly. However, what you are speaking of is a fundamental sense of tonal balance in one's ear, which is not the same thing at all, and so the answer would be no.
As to your violinist dealer, who knows what sort of background he had as a violinist before he became a dealer. If he had played full time professionally, I seriously doubt he would have "lacked a sense of overall tonal balance." Professional musicians generally have very good ears, and are very sensitive to pitch, timbre, etc. However, there are certainly some professionals I know who don't have particularly good ears. Perhaps he preferred less bass in his systems since he would more naturally tend to focus on the higher frequencies first, being a violinist. It would not have anything to do with where he sat onstage, though (he just may want to hear the violins better and get rid of some of that pesky interfering bass - let's face it, violinists tend to be the worst of orchestral prima donnas). Seriously, when I was referring to knowing what music is supposed to sound like, I meant out in the hall, not on the stage. We must always be aware of what we actually sound like out in the hall, as it does not sound like that onstage. And our own instruments sound different to us up close than they do to you in the hall, and we have to be just as aware of the latter as the former.
Another possibility. One unfortunate side effect of the job is that we will all lose about 20% of our hearing over the course of our careers. This will happen mainly at the high frequencies, though, not the low. Perhaps, if he is older, he wanted to hear less bass so he could continue to hear the treble better.
Another obvious possibility, if you will forgive my mentioning it, is that his systems sound fine, and that your expectation of bass is different. Many people nowadays, including audiophiles, have become accustomed by rock concerts and movie theaters to the sound of gigantic, grossly amplified subwoofers producing bass sounds that are completely unnatural, at least in terms of acoustic music, and when this artificially boosted bass is not there, they miss it, no matter what the context. This sound is also unfortunately created far too often and totally unnecessarily in symphonic concert halls via amplification, usually in pops concerts, a practice we abhor. I seem to remember another thread recently where someone was bemoaning the fact that many kids today have no idea what real live acoustic music sounds like, not just because of the above reasons, but also in the context of digital compression. We could go on and on about that, which is getting way off your topic. I bring up the possibility mainly because you used the words "dramatically devoid." No offense is intended, I am certainly willing to give your ears the benefit of the doubt. :)
