I've heard worse singers than Stevie, can only be honest and say that, to me, E. Costello is one of them 🙂....(I saw E.C. live in the 70s as part of the Stiff records tour....but I was paid to be there).I find him very patchy too, but am puzzled by his singing as being viewed as poor. This thread sent me to Talking Book, and whilst Superstition is a great song, As from Songs in the Key of Life is a sterner test.
Neither get anywhere near Elvis Costello's Pump it Up, or Muse's Madness or New Born, though!
As is always said, "each to their own" 👍