I don't believe that Jet Black (aka Brian Duffy FYI) is a bitter/angry old man (I'm paraphrasing here, not quoting) at all.
I just think he's speaking honestly from the perspective of someone who's 'been there, done that'. And done it the 'traditional' way, i.e. playing hundreds of small venues (in particular, the band were part of the burgeoning 'pub-rock' scene of mid-70s London) and in doing so attracting new fans all the time; and all this long before they got a sniff of a recording contract.
And being unable to afford a roadie, they also set up their own equipment for a long while. Rather quaintly, they didn't use the ubiquitous Transit van to transport their gear around from venue to venue, but one of the ice-cream vans from Jet's successful fleet. The band also used Jet's off licence business as their HQ.
I personally agree with a lot of what he's saying, but regardless of that, I think his opinion is valid based on his long career and involvement in the very business he is forming that opinion on.
I fail to understand the argument that record sales (by his band, or by other groups) in some way invalidate his comments.