You seem to have some knowledge of what goes on in an amp, however, it is incomplete or inaccurate.
Dude, what you are cranking up is the preamp gain NOT the power amp gain.
So, what do you think happens in a non-master volume amp, like a JCM 800 1959 Superlead, when you turn up the "Volume" knobs? That's right, you are "cranking up the preamp gain". But, at the same time you are also feeding more signal into the power amp section ("cranking up the power amp gain" i.e. power amp saturation - a different debate altogether). Master volume amps can accomplish the former without necessarily doing the latter. Hitting the sweetspot in an amp is simply finding the spot where you like the tone and feel. For non-master volume amps, this could mean turning up to stadium/arena volume levels.
In that case it's neck to neck with a SS amp.
That would be wrong. I suggest you read up on solid state harmonic content vs. tube harmonic content. Simply put, when pushed into clipping/distortion, tubes produce harmonics that are more pleasing to the ear, predominantly the 2nd-order harmonics. Transistors on the other hand, not so much. But that's not to say transistors can't be made to sound good.
You are better off using a multieffects with real tube into a SS than lugging around a back breaking tube amp head and cab.
Multieffects* with tubes in them actually use the tubes as an input buffer. Buffers have a gain of 1:1, meaning, the tube isn't even going anywhere near clipping. You won't be having any of those even order harmonics to benefit the sound. So, "better" is a subjective term.
"Back Breaking"... well, you know what they say, "No pain, no gain." We all have different priorities, even with music. Some would prefer the ease of bringing a lightweight multi + ss combo to a gig. Some would prefer to bring a rig that they enjoy playing through, even if that rig is a monster 100lb rack system.
