Remember that there are now basically no ties between province and Super Rugby team, except for arbitrary ones.
Even ignoring that, Cruden, Smith, Dagg, Guildford, the Whitelocks and Crosswell were all lost prior to Hammett and co. having any influence. Fitzgerald was picked up by a particularly intelligent coaching contingent, and probably most people around the country would still rate him below the likes of Eaton, Broadhurst and Thrush.
Nonu and Hore are understandable (particularly Nonu). I think the major problem is that the Hurricanes are holding onto a bunch of older journeymen players who are never going to amount to much more than they already do. Thrush, Broadhurst, Goodes, Lam, Smiley etc. are all fine players, but they aren't going to improve any more, they've plateaued, so you can't expect the team to improve that much. Obviously there's room for growth with players like Barrett, Ardie Savea etc. still young and promising. But there aren't enough of them. The Hurricanes are actually a lot like the Crusaders, except their players are just worse, on average. George Whitelock is not going to get any better than he already is, but his current state is still above Levave, Lam and the like.