The thing that works against the "mismatch" argument is that the ascot guys are lined up fairly uniformly, separated by the untailored uniformed guys who are also lined up fairly uniformly, etc... IE: the uniforms do seem to indicate something... what that is, who knows, but it's my assumption it's more along the lines of rank or station than just that some guys could afford a more tailored suit and others couldn't...
I look at them much different than a guerilla force though... To me the base/hidden fortress we see in ANH that's moved to Hoth in ESB is the Rebel's attempt at incursions into the inner rim worlds, and into the heart of the Empire... A guerilla tactic of hitting major space lanes, trade routes, and planets/military instillations that will gain a lot more attention than duking it out in the Outer Rim, the Fronteir Worlds, unexplored space, etc., where I feel things have gone on for most of the war till just before ANH.
The Fleet Trooper helmets are a mix too... Some have what seems like a solid visor too, not just missing it but it's there just all white. Then there's some with visors down, some up... And how do they put the visor down and/or up? Weird. I could see the helmet though transmitting some data tot eh wearer like a simplistic HUD. That's not out of the realm of reality now, much less a technologically advanced fictional galaxy, and the Stormies supposedly have the same deal going to some extent.