I haven't checked every goalie in the league, but without even checking this is slightly misleading.
1) The random year of 05-06 seems odd? Why that year?
That's as far back as AHL.com goes. I also think it's a good stopping point because the game has changed a lot over that time - scouting wasn't as far-reaching the further back you go, and so you might run into potential survivorship bias issues.
2) The vast majority of the starting goalies in the NHL were either already in the NHL at that point OR played in Europe not the AHL OR played in college so their AHL years were when they were 22 or even 23. Very few were in the AHL and as young as Blackwood was last year. So comparing their AHL numbers isn't a direct comparison.
That's a good point, but you're still exaggerating this effect. Any goalie who came from major junior who didn't play an overage season played in the AHL at Blackwood's age. European goalies at age 20 are by and large playing in comparable leagues - the KHL and SEL aren't that different from the AHL. I doubt you'll find many successful NHL goalies who were on the verge of washing out of one of those leagues at age 20.
3) Even given that: Ben Bishop as a 22 year old goalie in the AHL had a save % of .897. At the age of 21 in the AHL Robin Lehner had a gaa of 3.26.
Blackwood had an SV% of .882. You realize that the difference between .882 and .897 is the same as the difference between .897 and .912, right? That Blackwood was not only bad - he was beyond bad? An AHL season can be short, and it can be especially short when a goalie isn't getting it done. Either way, it took Ben Bishop until the age of 27 and 2 trades to establish himself as an NHL starting goalie. I don't think that's what we're looking for from Blackwood.
I don't care about GAA. Goalies have almost no control over how many shots on goal they face.
4) The entire goaltending in Bing sucked last Year. It's possible they all sucked because they suck. And it's possible that there was a team defense issue there.
Blackwood may indeed be nothing but I don't think last season is enough to conclude that. He had success in the AHL the year before, so I don't think his talent just left him.
No one was as bad as Blackwood, or even close. If Blackwood put up a .900 like Appelby, that's not great either, but I wouldn't be wanting the organization to write him off. The point isn't that Blackwood can't be a decent AHL goalie - he probably can be. It's just that he almost certainly cannot be an NHL goalie. But hey, if he puts up a .915 next season, all that's forgotten.