I looked, but haven’t been able to find the full text of the introduction you mentioned, so I can’t speak in anything but general terms, but frankly I have never cared for Fred Allen, and it sounds like Shepherd didn’t either. I won’t disagree that his comment might have been out of place in that introduction, but I won’t disagree with his opinion.
Do you have a link?
All I remember of Fred Allen is his phony Chinese accent when playing a detective.
A classic instance of offering a slap in the face with nothing to back it up. Fred Allen may not be to everyone's taste, I enjoy him but I get why others may not, but if that's all Shepherd could remember of Allen it's plain that a) Shepherd was not offering an opinion with even minimal reasonable qualification, and b) he didn't really get that Fred Allen's cumulative style wasn't anything like Paul Rhymer's cumulative style,. and that it would have been foolish to link them in the first place whatever Shepherd thought of Allen.