Overall impact.. as in terms to the entire defensive unit. I would say that both had a huge impact to the defense.. edge to Cullen but not by much.
I think it was apparent that without Jenkins ability to create a push, the entire defensive front was impacted. Much in the terms of when Ted first came and we lost Rivera and Wahle. We undervalued their impact on the performance of the entire group.
Simply, the other pieces just couldn't replicate the same consistent interior pass rush and the protection schemes of the opposition could be focused on the remaining threats.. Matthews and well to a lesser degree Raji. Wynn flashed here and there, but not consistently. Pickett & Green are more of pluggers... CJ is still a work in process.
IMO, that set in motion limitations on how much pressure we could apply and it got Capers to adjust and maybe try and overcompensate some.
Now.. Collins hurt in a couple of different ways.. the greater being two fold.
1) Communication ... on field and in play.. Woodson and Williams could rely on Collins being in place correctly and could play off that some. With him gone, you seen both Morgan and Charlie out of place at times.. forcing the corners to play more straight up. Woodson was exposed at times.. showing a little loss of step. Williams simply couldn't play his press game because of the shoulder and exposed his lack of recovery speed. Shields regressed.. basically a recipe for bending greatly.
2) Collins range.. hall of fame type range, could erase a ton of mistakes.. simply the remaining parts couldn't duplicate that.
IMO, Collins was a HOF type physically gifted athlete.. but I would not consider him a HOF candidate over his career. If he could have kept playing.. who knows.
"The oranges are dry; the apples are mealy; and the papayas... I don't know what's going on with the papayas!"