We all make our own judgements, but "he has never been a good keeper, even at Championship level" seems extreme to me. Would Southgate have called him up for the England squad if that were the case?
Well considering he hadn't even been tested outside the Championship at the time, and was 4th choice after Butland who was playing for a poor Championship team, yes.
Although I will concede that for the second half of 17/18 he was performing at the level of a good Championship keeper. Whether performing at that level for barely half a season actually made him a "good keeper" is debatable I suppose