I have had the same issue at band practice and don’t think it’s normal. I have tried everything as well and had to max out the Kemper power head until it shorted. I built a 4X12 Kemper kab and thought that would do the trick, and still the same problem. Because sound is not projecting forward like a guitar speaker would normally, the sound does not cut through the mix.
My guitarist has a mini Mesa at level 1 and was still cutting through more than I was.
I have now gone with a 2x12 mission Engineering cab which does not colour the sound and at the same time projects the sound forward which I am now able to cut through properly but barely. I had too turn up the Volume to max with the rig volume and now I have my max volume on the Kemper almost up all the way and the wattage meter goes to almost. 600. It’s loud but not as loud as you would think at that level.
Standing in front of the amp at that volume, it was still bearable which is the problem. The 600 watts should be impossible to listen too from up close and with the Mesa turned up to 150 watts only, I was almost deaf lol.
So not sure, something to work on for future models perhaps.