DDG is a goal keeper that has a style of playing that makes him shine, but doesn't really help the defence. He is the best shot stopper of all time imo, but non-existing in the box, non-commanding, no leaderships skills. At his peak, he saved us many times, but many of those saves wouldn't have been necessary if he had been more active in the first place.
I remember one of his best seasons when Smalling, Lindelof and Jones paired up as CBs. DDG made an increadible amount of super saves. Then there was Ederson at City, who conceded just as few goals but withpout the saves. Everybody said DDG was superior, Ederson played in a strong team and didn't need to do any saves, etc. But fact is, Ederson made 40 sweepers clearances that season. That's more than one per game and most of them would have resulted in a 1v1 with the goalkeeper. To me, the difference was obvious and I could see why none of the big, dominant teams playing a high line were interested in DDG.