I did not put either Frentzen or Alesi on my list because I thought that neither had achieved much in the 2000′s, although both were obviously quite talented drivers.
About Rosberg, I think he is pending. It’s quite a shame though, as I think that he’s a better/faster driver than Button, who is a champion. Unfortunately, in Formula 1, talent is often not enough. If Nico got a Brawn-2009 level car, I have no doubt he’d win the WDC.