Agree that I appreciate the explanation but still struggling to get it.
If monitoring is that important, why not set up an on stage monitor with the KPA? That's why I have the power rack and Kabinet so if I want on stage monitoring I know its very similar, plus less equipment. Alternatively I've just bought the player, added a £65 Harley Benton power amp and I can run that through any cab or Kab - works brilliantly. I think that solves your problem full stop doesn't it?
I might be wrong but most pro guitarists I don't believe use a mix of the KPA and amps as you suggest ( although I might be wrong and there will of course be somebody doing it).
Yes some pros take multiple amps either for different sounds and sometimes ( but not that often) to blend sounds. Most pros would not have a different on stage sound/solution as FOH mainly because they use IEM's.
Some people also use valve amps as their power amp, so still use the amp sim but use the valves to add warmth - not something I ascribe to but this is more common.
I bought the KPA so I don;t have to lug another amp around and I think many people are the same, so your use case I think is pretty niche.
As you say though, if its easy then why not. Perhaps others will disagree and see the need that you do