Jack wrote:-
thank god he never persuaded any of his epigones to follow suit.

I'm not sure that "epigones" is the right word here, Jack. To me it carries quite a perjorative impression. One of my dictionaries defines it as "an inferior follower or imitator" I think that "adherent" or even "follower" on its own might be better in this context.
If we consider the members of the Critics Group, though there are some who sounded, certainly at the time, like "impersonators", it is not difficult to name people who were active in taking what MacColl had to offer and then built on it to make themselves more rounded performers. Names like Frankie Armstrong, Bob Blair and Sandra Kerr come to mind as those who blossomed into some of the finest that the folk scene has heard.