While more frame/structure rigidity can't hurt, my understanding of panel gap issues is that they typically have much more to do with the variability of the panels themselves, rather than the frame they are attached to. Panels are stamped and formed from thin sheets, and there can be many factors that induce variations: stamping spring back, stamping pressure, tooling wear, temperatures, pressure selection, alloy variability, etc...
On the other hand I expect a frame welded together from extrusions/stampings to be pretty tight in terms of tolerance, cooperatively speaking.