This has been adressed long ago. From what I can remember from an old forum post by chadz, that he understands that the multipliersystem is bs and they do try to rework it. Woulds/shoulds/coulds about the xp/gold gain are unneccesary cause its an old age issue that has had tons of suggestions over the years. One more flawed than the last. Until then, you just gonna have to live with it.
Well, I suggested some time ago that your equipment is not determined by money, but by skill point investment. The more skill points you invest, the higher your budget and/or the more slots you have. Since your equimpent is directly affecting your effectivity, it needs to be balanced by something else which also affects your effectivity, to have some kind of tradeoff and to keep the levels equal. And the only other thing besides equipment (and skill, of course, which is unimpotant in this case, though) are your character stats. So either have a character with good stats and bad gear, with good gear but bad stats, or something more balanced. It's a way more persistent (no "good" and "bad" loadouts needed) and predictable system, it limits equipment more effectively than the upkeep system (whoever does trading on the marketplace is unaffected by upkeep), it allows much more freedom (heavy cav, plated infantry, etc.) without destrying balance, and it supports more character diversity. And last but not least it's fair, because everyone can afford the same. Strat players, clan members and whatnot don't have unjustified advantages.
I don't see where such a system can be more flawed than the upkeep system. One time chadz even admitted it would be worth thinking about it, but since the upkeep system was already implemented it was too late, anyway.
(I am referring here to the upkeep system, which is the big problem, not the multiplier itelf. The multiplier is only the means by which the problems of the upkeep system (= the gold income) are delivered.)