There's a great deal of speculation around what Sarah Makem said about her son's singing - I wonder if anybody can back it up with solid information - I can't.
I (and the person who first told me of it) always assumed that it was that she felt that he had no feel for traditional songs. It wasn't that he couldn't hold a tune or project his voice - he certainly could.
It's always made sense to me that Tommy Makem was one of the people who became swept up in the comemercial side of folk singing, donned the uniform (in this case an Aran pullover), and, along with the Clancys became a 'formulaic' singer, applying a set technique to everything he/they did.
It's like the old musician said in the film, Round Midnight - "Your notes are fine, but where's your story".
I have to say that 'group' singing of traditional songs, with very few exceptions, never worked for me on narrative songs. There are examples of traditional songs that cry out for group treatment: shanties, waulking songs, some of those connected with rituals or customs, but as far as 'story' songs go, I have always thought that an individual approach is the most effective. Anything else becomes too much of a compromise on both technique and interpretation.
My feeling - for what it's worth.
Jim Carroll