Well, my 2 euros.. my own, personal, subjective, relativistic opinion.
.. Profiled many amps I've owned... Oranges, Marshalls, mesas, laneys, all the while constantly being bombarded with the idea that profiles, when done right, are identical representations of a source tone at a given point. If not, the issue must by definition have been user error and/or one was paid by fractal and/or the differences were so small no sane person could possibly care.
.. Yet... I'd hear the same shortcomings elsewhere as well... And I'd have one producer or another confirm my observations, as did some profile sellers.
What I'd see with my own profiles is dips in mid lows (100-120), a weird cocked wah effect in the mids.. and I cannot truly say I was happy enough with these tones, most of the time at least. Yes, given a certain type of playing and PU they could confuse the listener. But as soon as I'd turn on my amps.. it would be "game over" in terms of feel. The depth I'd expect from these amps just wasn't there. It wasn't simply a matter of "just a bit different, but equally as good" either.
... And then.. I finally got the chance to try match my amps using an axe fx 2 we had at studio... Getting ready for that "fake, digital-modelling sound" that would make me puke, if dominant opinion in some parts of the web was to be believed, I expected the worst.
Oh well, was I in for a surprise.
Shooting IRs and tone matching, then comparing to my amps, I preferred the axe results to Kemper much of the time. More depth, less "cocked wah" focus, but most importantly a greater ability to fix problematic-to-me parts of the sound. Where as with Kemper I'd profile again and again, trying to dial in the amp a bit different just in case I get a more accurate profile, these problematic areas were fixable to a greater level with axe via the very convenient editor. Post controls of Kemper such as "definition" are cool, but not as clinical as what's available in axe, generally speaking.
Then the lack of editor became a pain on the shoulder quick.
There was another plus here with fractal. Axe fx allowed me to finally use dual distorting stages (say preamp + power amp disrortion) that Kemper wasn't designed to profile. Not everybody cares about these tones, granted, but I love having such control over a preamp and a Poweramp without being scared of where the "point of no return" comes and profiles go bollocks. Profiling my orange properly with master cranked was not possible for me... And while axe wasn't a perfect imitation of that tone, it definitely got closer, sounded and felt better to my perception.
Of course It wasn't all Rosey with axe either.
I did have a couple of amps in that I couldn't quite emulate as well as the kemper, using axe 2, due to lacking internal amp models. Perhaps it could have been done better. In my case, I felt the profiles were closer. The way Kemper does what it does, other than EQ matching, can also mean achieving good tones pretty fast, considering one has amps sitting there ready to be profiled -- and lacking an internal amp model isn't an issue the same way I felt it could be with axe.
But that's the thing.. even if axe doesn't have built in models for everything in existence, it's not like kemper would profile all Amps equally well. Add to that how innacuracies, imo, tend to be quite consistent along profiling different tones, and you kind of end up with more of a homogenous feel from profile to profile compared to axe Amp sims or the real amps, for that matter. It's relatively evident in the mutes and single notes for me.
Then i also factored in the fact that even altering gain levels on Kemper to fit my pickups = not a realistic representation of the amp.. (which can be a plus in some cases, but most often for me not so).. and editor.. man, there is a lot to appreciate about axe fx.
All that said I still like kemper quite a bit. Even with the shortcomings I think it has, it's a great unit, still able to do something nobody else does quite as well overall (and I mean calculating gain, ect, whatever goes on during profiling, which isn't only eq matching). I would have probably not used axe as much had it been for Kemper being more accurate in my profiling sessions, because I've always like the concept of profiling.
But after using both devices for quite a while, as well mostly real amps.. I've been closer to axe for a while now. I still feel that the amp Sims tend to lack some depth compared to the Amps I've compared them to (yes, even amps comparable to the amp sims) but the range of options usually has gotten me where I've wanted to go.
Perhaps this changes in the future if Kemper becomes more accurate and I think the feel is more accurately representated.. or not
Who knows what the (gear) tide may bring. And yes I still prefer real Amps to all other choices !
Cheerios