I'll start by commenting on your list:
Jimmy Tarbuck - His act seemed out of date even when he started performing
Lenny Henry - An outstanding talent, with excellent stand-up comedy, in his early days. But he can't act (as anyone who has listened to 'Rudy's Rare Records' on the radio will testify) and he seems to have lost the plot when it comes to stand-up.
Frankie Boyle - Occasionally funny when a guest on QI but he has limited material and he fails to realise that an essential element of comedy is to surprise his audience. There's no surprise if you use a 4-letter word in every sentence, or if your material is otherwise totally predictable.
Lee Mack - Some of his stand-up routine is amusing but he definitely can't act!
Jo Brand - I quite like JB but her material doesn't seem to have evolved much over the years.
Sue Pollard - I don't think I've ever seen her do stand up. She was excellently cast in Hi-de-Hi but has looked out of place in other programmes.
Miranda Hart - Her stand-up routine is just about bearable but, again, she can't act.
My least funny comedians:
Vic Reeves, Bob Mortimer and Johnny Bloody Vegas!!!