We don't have the talent in the secondary. the 3-4 would be much more effect if we had any support from the secondary. Not being able to cover tight ends isn't all on the linebackers either. Safeties are often matched up with tight ends as well as Sean Smith.
No one in this scheme needs to be double teamed.... really? Cam Wake doesn't draw double teams on a consistent basis?
Look, you stated this team wasn't built for the 3-4 and that's just flat wrong. Now you've changed your argument to them not being able to play it. Like I said though, it'd be a completely different defense with any degree of competency in the secondary.