His rookie season ended up being an anomaly, mostly because everyone in Washington, including RG3 himself, knew that if they kept running him out of the pocket, then his career was going to be cut short. What they didn't know was that RG3 is so bad in the pocket that his career was going to be cut short, regardless. RG3's NFL career was always on borrowed time. and no, the injury didn't prevent RG3 from becoming the "next big thing" Being a shitty passer did that.
When you're comparing the professional careers between RG3 and Cousins, there's no comparison. Cousins is objectively better.