I agree that quality is a must, and that overexposure doesn’t help, though some book promoters would argue that it takes a year or longer for most books to get going. That may be true but I’m not convinced.
We know of quality books that don’t get the attention they deserve. Some “terrible” books do quite well.
I think it’s difficult to say what makes a book sell, even the experts get it wrong. Quality however remains an indispensable ingredient.