I think one of the persistent 'mistakes' Dai makes is to 'play it safe' in selection choices (next game and next season). By that I mean, open himself up for less criticism if a 'gamble' (in his eyes) doesn't come off. This is only one or two players, but, in my opinion, and that is ALL it is, the backs are where the selection mistakes are being made.
Buy in a big name rather than promote from within (e.g. the academy), and use 'more experienced' utility players in the backs rather than youngsters who actually play in that position. What some of us call a failure to develop the academy.
Those early season team selections were beset with injury problems, but even still maybe did not hit the right balance between experience and youth. I am not sure he made any mistakes then, he simply didn't have the right options available.