I recognize that you think your tube output section makes your Kemper better. For your conclusion to be factual, you are implying that the your tube output section PERFECTLY corrects all of the errors inherent in the Kemper as is. Did you indentify all of the errors in the Kemper and design a tube output section that perfectly corrects the errors or did you just get lucky or is it just not an accurate statement? I know which is more likely. You state "ears mean everything" and "the guitar experience is about feel as much as sound". Those two statements don't logically make sense. I think you must mean that both matter. Or can you hear the feel?
Again, YMMV. And again, just making a note so others that read this thread understand that there is a rather large difference of opinion on this topic.
I think this is why there is a large difference of opinion and as per usual the answer is possibly somewhere in the middle...people talk in absolutes when there are so many variables such as:
1) No such thing as exactly the same sound, there is always some variation
2) I think psychology plays a much bigger part than people realize. Unconscious bias ( I want it to sound better so it does and vice vera), how we feel, etc. Our ears are imperfect devices attached to a brain that can alter perception and reality
3) Valves are not perfect. They are the sounds we have come to know and love but they have issues, artifacts as well etc. so for me "add a valve" is rarely a fix all..Its seen as the special sauce which has some truth but also a lot of folklore. This is why blind tests are always interesting...
Personally I agree that a valve amp is not needed. We have a device that mimics a valve amp to a high level of accuracy and then add a valve amp, which to me will certainly add something. As you say, very unlikely it perfectly fills the gaps and so more than likely adds " even" more. Whether that is positive is another debate.
Its the old adage, if it sounds good and inspirational to the player, that's great. Is it necessary? I think that is the point...