Can see three reasons why fans are too critical of Dias.
First, they prefer another player, Stones (when fit) or Khusanov, and are unhappy Dias has been picked instead of him.
Second, they are clueless regarding the actual record with and without Dias since the start of last season. Hint: it's much, much better with Dias than without him.
Third, they don't get the role of leadership, because it's less tangible than blocks, tackles, speed, etc. The perception that Dias is slow overrides his other qualities.
He won't be faultless when he returns, but as a whole we are a better team with him.