I have the same experience.
I would belive I should be able to get the same sound as in the samples in YouTube or Soundcloud as long as I play the samples trough the same monitors my Kemper is connected to. I play at same wolume and different guitars and pickups. But it sounds very different.
I fieel it gets closer if I play at gig volume but at practice level the samles is much fuller and more clear imo.
I heard from profile authors that the samples is direct recordings from the Kemper, but to me it sounds like it's recorded from cabinets or bigger monitors cranked.
I don't know if that make sense or other have same experience....
Volume makes big difference imo