Part of the 5% issue (if it exists) is us guitarists' conditioning to solid state and digital marketing for decades promising "just like a tube amp.".
It does exist, although I think everyone is missing it. It has nothing to do with copying warmth or quality.
The missing '5%' (or more) is that tube amps are like people ---- > moody. Kemper takes a 'snapshot' of your tone and you stay at that snapshot, a perfect pleasing tone all the time. It may be your best tone, but it is -that- tone all the time. Solid state is similar, but it isn't a copy of your fav tone, its just a tone. But the same where it is like it is ---- > all the time.
Tube amps change all the time like the weather. They warm up, sound cold, lack something, sometimes sound even beyond what you'd imagine. Then crap again. A constant battle. You try pedals, whatever, to compensate because of the guitar(s) you use, or just to add constant sparkle, etc., then you throw it all out and start from scratch again, fall in love again, a nice clean amp sound playing direct.. Then you have a bad sound day and what to kick that B_tch to the curb, buy a new amp and start again. Sometimes you have many amps, like dating, you just pick one you know will do it for you that day. Unless it sucks and you plug into another. And another. Then try one of them you haven't seen in a while and magic!! Whoa! Why did I want to sell this POS?!?! It's awesome! until tomorrow....
It is the tube amp's imperfection that we are attracted to. Like a junkie that keeps looking for a repeat of that first high, but never obtaining it. Or a smoker trying to get that first cig buzz, whatever... Sure, you can buy the 'patch' but is it really the same? You can drink diet soda, but is it really like a real soda?!?
When you have something that never changes on its own, you grow used to it, and naturally, get bored with it. Your ears pick up on the similar details like a chick you get bored with and want to move on. Or maybe try to change her?! ;-O You want the thrill of having to fight something to see how far it will go. You get in your car and exceed the limits, not know if the engine will blow the hell up. That is the fun of tube amps.
Safe amps seem to give you the deal but you always think something is missing, well there it is. The only way to change digital stuff to that is to come up with some 'humanizer' or 'real world-izer' to simulate the subtle moody tube amp circuit that we constantly try to tame.