I'm sure some will tell you there's a "baked-in" tone, and that it is quite scooped when run "flat" (by which I think they mean knobs at noon). You can find lots of info on TB about what is an actual "flat" setting with GK amps, and it's no more scooped than any other when set properly. What I've found is that I can get almost any tone I want using the EQ. That's what it's there for! Sure GK has a distinctive sound, that's why we use them! But it's also as versatile as any amp I've used - you just gotta play with it.
That's what I came to hate about the Streamliner no matter what you did you couldn't get that scooped sound out. I defended it for a while as it is a more authentic tube amp sound like a Bass 400 (really scooped). I wouldn't call the RB tone scooped by any stretch of the imagination. You can get a scooped sound out of an RB but it still retains that signature punch. Got to love that sound.
This weekend I used my GK MBF500 and two GK 112 cabs for two shows, next weekend its going to be the 700RB and two CX210 cabs. That's my favorite all time tone, the signature hard grind is unmistakable!