It's a bit early to write them off. Connors reached 10 at the age of 21, the equivalent for Milos would be the upcoming French Open. Connors was also the only one of his generation who did anything (the next previous one being Stan Smith in 1947. So Raonic still has another 6 months to move up to the top 10 to keep with Connor's career pace which is still very possible.
That's why I said "we'll see", and that they're underwhelming as of "now". Who was I writing off?
I believe this generation faces a particularly unique predicament in that they're entering the pro tour when it's more physical than ever. It's rather common these days that younger players, unless truly extraordinary (see Djokovic, to a lesser extent, Murray), need time to adjust to the physical and mental demands of the tour. One of the reasons I think Raonic has sprung up so early is because he's physically more mature than his peers, some of whom may actually be more "gifted" in some respects.
Raonic also made 4R at AO '11 and Berankis made 3R at the same tourny, not 2012. And yeh, you might as well add Janowicz.
Corrected Berankis' year, and added Milos' second R16. The reason why I didn't add Janowicz is because he hasn't even had a full year on tour yet, but he definitely deserves a spot on the bubble at least.