Tom Abraham has run FOH for a who's who of rock and metal legends for decades. He knows what he's talking about. So when he says that the Kemper is the best modeler/profiler sonically but that all of them are inferior to a tube amp in the mix, I'd listen to him.
And he's not just talking about frequency response and "EQ". There's also compression and transient response at various frequencies and how those things affect the ability of the guitar to cut through the mix even though they may "sound" identical.
He's not dumping on modelers, or profilers. He's just describing his experience, which he admits completely surprised him. He thought the guitars sounded IDENTICAL when isolated, but for some reason they disappeared in the mix.
His specific experience with the Plexi in the mix was with the FAS modeller and he prefers the KPA from what he says and perhaps the same situation - live mix with a KPA Plexi profile - that issue would not apply. Seems like a great many artists from MBritt and Bert to household names are touring on big stages with the KPA and sometimes the whole band - bass and guitars are using them.
The point you make about transient response wrt to compression and transient frequencies is an interesting one. The study of human response to sound shows that we are especially attuned to the attack transients of any sound and devote a lot of neural processing to just these parts of any sounds we encounter. From an evolutionary perspective, I guess we can surmise that surviving predators and enemies sneaking up on us was pretty important for our ancestors. Anyway, that is how we are built and it could indeed be a critical part of the way we process the parts the various instruments play in a mix.
Just in general wrt to some of the other comments about moving air. As far as a mix goes - a mix that you can listed to on monitors or with cans is all about audio - 10 or 20 Hz to - 20kHz , which is to say radiating waves of variable air pressure that excites your tympanic membrane. Invoking sonic impulses that you experience in close proximity to amps or kick drums or whatever in a live situation - trust me I have felt that stuff myself - does little to explain what is audible or not in a mix of recorded material which might be playing back in a booth or control room at 85 dB or so.