There isn't a universal definition of a "bust" when it comes to sports. It should be all about actual performance vs. reasonable expectations IMO. In Pouliot's case, being picked 4th overall and never scoring more than 20 goals or 40 points in a season, and the fact that he only played 65 NHL games for us, does not meet expectations of being that selection. So I would consider that a pretty big bust.
Even Granlund would technically be one IMO, though to a much lesser degree, as he was drafted to be at least a good top 6 center for us for what was hoped to be many years. He was only a center for a little less than 2 seasons worth of NHL seasons, and a pretty mediocre one at best. Now, he salvaged some of his value when he moved to the wing, and that's why he's less of one than Pouliot or Shepard were.