sixtonoise,
RE: Uberschall. It's a great amp. So are the Ecstasy and the Herbert. So are the Diezel VH4, the VHT Pitbull, the Fuchs Tripledrive Supreme and Badcat amps. I've played each of them, and as great as every single one of them is, none of them let you use the full gain of the amp without sacrificing tone. The technology apparently just isn't there yet. That's okay, because it's also fun to have the flexibility that a good overdrive/boost offers anyway.
Your description of the AX7's in your Rectoverb was great, although I am already aware of the structure and function of cascading gain architecture and was being somewhat facetious in my analogy. Still though, the purpose of each gain stage isn't simply to shape tone, especially since the tonal variance of the tube isn't very wide to begin with. It's primarily to provide additive gain to the preamp signal and, unfortunately, we're not there yet where all of the gain from all of the preamp tubes can be brought to bear without sacrificing tonal clarity and dynamics. Maybe we never will be, given that tube technology is quite old and may have certain inherent limits, but we can always dream.