Except that Peyton Manning is not a part of this conversation or comparison, but nice try.
Cousins has only started 6 games, so it only makes sense to compare his 6 starts to RG3's first 6 starts, the big difference of course being that Cousins has had more weapons to throw to in his starts than RG3 did at the beginning of 2012. I mean, how do Pierre Garcon and DeSean Jackson catch only a combined 3 balls last night? Bad quarterback play, that's how. Cousins has "career backup QB written" all over him. RG3 might very well have "injury-prone QB" written all over him, which isn't good either, but from what we've seen out of both so far in the NFL, RG3's best is far better than Cousins' best, and Cousins' worst is way lower than RG3's worst. In other words, RG3 has a much higher ceiling, while Cousins has a much lower floor.