I owned an Ax8, FM3, FM9 Turbo & the Axe-FX III. All brilliant. Unfortunately, I’m too thick and prone to “hey, what if I…” so I spent more time basically UN-F’ing stuff that was fine, sounded great, etc..
FAS makes amazing stuff. If all I did was studio stuff or I had a set of songs I played (ie Metallica, DT, or any other large touring act), maybe I’d still own/use that stuff. I play in a variety (covers) band that I need a clean sound, a dirty sound, a dirtier sound & a lead sound w/fx to taste for each. The QC does that for me with a minimum of time spent dialing, refining, dialing, deciding, second guessing. All of this is a me problem, not a FAS issue.
In terms of high gain, you can surely dial in high gain sounds on both, but you can adjust tons of parameters to create something truly unique with the FAS. I always just made stuff sound worse when I tried, though.
Customization is better w/the FAS stuff. I wish NDSP would pay attention to that kind of ‘quality of life’ stuff, even more than adding new amps, fx, etc.
Can’t speak to quality issues, my QC & Nano are great and all the FAS stuff I owned was great, too. My only complaint about FAS stuff was it seemed the updated hardware (turbo, mk2, mk2 turbo, mk2 turbo turbo, mk2 NON-turbo w/bigger scribble strips, etc) was always released about a week after I ordered/received the ‘old’ version. But maybe that’s the same as NDSP’s ‘Soon’?
FWIW, I sold all my FAS stuff (I try not to keep gear that isn’t going to see regular use). Well, almost all. I still use an EV-2 expression pedal w/my QC.