The 1971 Baltimore Orioles would like to have a word with you guys. Palmer, Mcnally, Dobson, and Cueller all won 20+ games, and Cueller had the worst ERA at 3.08. Also, the 1998 Braves: Maddux, Glavine, Smoltz, Neagle, and Millwood.
But it's easily the best rotation on paper of the past decade, and depending on the on-field results, could be #1. You have to figure Halladay and Lee should win 20 games, Oswalt can probably get 16+, and Hamels still has the ability to get 14+.