I think it's a rather useless description. I played the KPA through a guitar amp in the room and it sounded awesome. Took it to an outdoor even, sounded very thin.
I got a good sounding room. But outdoors.. Worse than if recorded by a mic losing the entire low end. So the room shapes what you think you are hearing. Too Many Variables of amp position, your standing position, type of speakers, etc.
The KPA is perfectly able to compensate for what you think you might be lacking. I don't think it's a "lacking" so much as a "different" because you are typically using different speakers.
I suspect the biggest culprit is volume. Most I suspect do not listen to their Kempers at anywhere near the volumes of their amps. Crank the hell out of your Kemper and tell me if it is missing something!
At that point, when your ears are splitting and the objects are falling off your shelves, you'll stop bitching about the "amp in the room" and go "Holy... SHIT!!"