I noticed this as well. A lot of the amp models themselves are really good. Panama sounded like total crap though and I can not tolerate the noise long enough to tweak it. I will tell you I did like the Smash amp a lot. I made a simple patch, starting with a noise gate, dual Smash amps, reverb and phase. I cut the phase to .7 and it really reminds me of a Randy Rhoades type sound. I forget where my drives are at the moment, but they are not totally cranked.
A lot of the Vox amp models sound pretty good too.
I too tweak existing preset patches, I do have the Glen Delune patches as well to work with.