But, bucky ... Arrington? Really? A UDFA cornerback/special teamer who was in at "DE" for a few plays at the end of ONE game and he makes your list of "pass-rushers who failed"? Sorry. No disrespect, but you might want to excise that one.
I understand your point, though, and if you want to expand the list to include non-drafted acquisitions, we're also talking about Mike Wright and TBC (who, IMO, was originally drafted as just a sub-rusher, AND brought back as a sub-rusher, but, through an unfortunate set of circumstances, ended up playing a much larger role than he was cut out for).
I'm not sure I expressed my point clearly. It's actually quite simple and high level: our 3rd down personnel is quite bad - to the point that BB tried Arrington there for almost a full half. So whatever the strategy has been, it's not getting it done lately. Which is why a lot of people including myself are suggesting a strategy of using a relatively high pick (let's just say top 50) to get an immediate upgrade at pass rusher who can potentially evolve into 3 down OLB. Arguably, Cunningham is such a guy, but he's not that great of a pass rusher.