The lack of a consistent pass-rush is also a reason a championship team could be held back. Redding has slightly improved (which isn't saying much), but he got gashed in the running game for most of the season.
Ngata and Suggs would be unstoppable if there was a DE on the other demanding some attention.
Other than Lewis, who isn't elite anymore our ILB's are also getting shredded in all aspects. Ellerbee is the only one with some talent, but he doesn't play very smart, and is in the doghouse because of it.
The lack of a #1 CB is definitely a problem but our secondary isn't the only weakness on the defense. We still have some good young CB's, but absolutely no depth at the DE position.
With that being said though, I would have be very happy with Harris(if he fell somehow) or Williams in the first.