I hear you and agree with all of the points you made about Collins. I watch about three or four of his games so I have a pretty decent feel for him. He's obviously a natural athlete who potential hasn't been reached yet and he's more of a natural OLB than Carradine, though Carradine has all the tools to be able to operate in space.
With that said, Carradine is also a one year start IIRC and a pretty raw player in his own right. Carradine possess an ability that I'm not sure Collins has, and that's the ability to be a dominant pass rusher. To be honest, him and Quanterus Smith (from Western Kentucky) are probably my favorite pass rushers in this draft - though I won't lie and say I've studied every guy. I think I read somewhere that the ACL is the only reason he isn't a top guy in this draft and it looks like that thing is healing up pretty well. I only need my weakside guy to drop into coverage less than 10% of the time - give me someone who knows how the attack "the source" as I call it. Carradine is that guy.