There are many areas of art where someone can succeed with a massive audience, because they are not expert, and their expectations are very easily met.
An excellent example is someone like Paul Potts who was canny enough to choose Nessun Dorma for his big number before everyone else did it, and he carried the audience along on the emotion of the song, regardless of the fact that an expert will advise that he is not a particularly accomplished technical singer.
But that doesn't matter, because his audience are not looking for expertise, and may not actually know the difference if they heard it - or even care anyway.
The same appears to apply to AA who has an audience who will like him because it is him singing, regardless of actually how good or not a vocalist he is.
It's not my area, so I can't comment with any level of knowledge or expertise, but as I say, it doesn't matter because people like him, and how he sings, so he does fine out of it.
All art is subjective, and one person's entertainment can leave others absolutely cold.