Guitar amps are all about getting the right kind of harmonic distortion, so of course the guy had opinions. But tube rolling is madness, avoid it at all costs.

In this case it was a very common swap, 6550->EL34 for Marshall JMP 50W. I ended up going for it (the existing tubes were damaged), it sounds great.

There is a whole range of useable distortions, so a lot of the opinions mainly boils down to genre bias.

E.g. to a metalhead, any tone that doesn't "chug" is useless, including something useable to a jazz fusion player.