I just stumbled across this thread while searching for something else. It remarkably resembles my most recent realization as well. Just can't get along with FRFR speakers anymore. Been a Kemper fanboy for over 3 years now and like you I've tried quite a few FRFRs. Some cheap some expensive (Headrush, Atomic, Xitone, Mission Engineering). Always felt like I was lacking. While I DO agree that you're losing a bit of that "Difference" factor when checking out different profiles when the cabs are included, I just can't get past how perfect and tight and realistic things sound with my Mesa 2x12 cab in comparison. It sucks. I don't WANT it to be this way. It just is.
I will say that in one of my tribute bands, everyone goes in ear (Except me as I HATE them with a passion) and we have very low stage volume. In THAT band I use my Headrush 108 up front and it does the trick just fine. For everything else, I'm back to being old school with a Cab behind me. I still go direct to FoH but I just PLAY better when I've got that feel pulsating behind me!
Hey it took me 8 years to come to this conclusion.
You, Sir, are a fast learner.