Well, he was forced into being a playmaker far sooner than anyone had hoped. I don't think anyone anticipated Nik would leave after two years, and obviously Caris went down early in Zak's sophomore year. To compound things, Walton was injured as well. I think by the end of 2015, he was playing some pretty good ball, and the stats bear that out.
I think there's a recency bias here in effect - he was up-and-down, and at times just awful, this past season, and that's what people are going to remember most vividly.
Right now, it all depends on his back. I think a healthy Irvin is capable of a 16/5/4 line, and shooting maybe .450/.400, which would be great for the team's prospects. If he's not healthy, though, that will really hurt us because he'll still get tons of minutes, and he'll still take tons of shots.