I find the "it doesn't push the same air" complaint a little uneven. Of course the Kemper isn't going to give you the same visceral experience as a tube amp through a proper cab, but when you play out, that "pushing air", "in the room" experience you get is only relevant to you. Your audience is hearing a mic'd cab through PA speakers, so it may as well be a Kemper in the end. There is an argument to be made that how your cab behind you blowing air at your knees affects your playing and enjoyment of the experience, but ultimately something that gets lost by the time it reaches an audience anyway.
They do have a point in that the Kemper's power amp is weak compared to a tube amps (and many other solid state power amps). I know they both have a power rack, but perhaps their experience would be different if they used the Kemper with a Matrix GT1000FX, which adds a lot more "tubey" warmth.
Neither the kemper solid state power amp or the matrix quite gets the job done for me when it comes to "pushing air" with KPA. The best results I've gotten have been using a Fryette power station. It's a tube power amp. Wicked. Side by side compared to Matrix GT1000 it was a no contest for me.