What this means is its possible to build a solid state amp that is every bit as smooth in the mids and highs as the best tube amps and leave nothing on the table in terms of detail, sound stage and the like, in such a way that vintage amps simply cannot compete (not that they sound bad, just they don’t sound as good). This is one of those things that is easy to hear and easy to measure.
If you are convinced that best amps can be measured, you most likely hit a goldmine of technical wisdom, although the term "smooth" might be not universal enough to define it. However, in my opinion, that is not even possible, especially because amps do not make sound on their own: the sound you hear exists in a relation to all component in the signal path. Insisting on individual component’s quality, as promised by manufacturers marketing materials, rather than emphasizing the signal path synergy is not the optimal formula to enjoy audio but, of course, it can be easily the most expensive one...