Tubes = distortion + noise.
They do not belong in a reference system.
not all tube amps are created equal, and not all listeners have the same system aspirations, not all rooms are the same size, and not all speakers need the same power. so dismissing tubes for a reference system is not right either.
if you consider an OTL circuit, then you are much more linear by eliminating the transformer. if you have a medium to small-ish sized room but love small combo jazz and small scale classical, then plenty of tube amps can be reference quality. if you use 105+ db efficient horns then all sorts of tube amps can be reference quality.
so even with the theory of greater noise and greater distortion (a theory) tube amps can certainly be great.
OTOH in a large room and expectations for full frequency and state of the art linearity on large scale music tube amps will struggle to keep up. could be done. OTOH with darTZeel i know it can be done and not have to live with solid state restrictions in musicality.