I'd disagree on your third paragraph. You can build a Seattle caliber defense if you hit on all your draft picks on that side of the ball in a three year span. Not all of those guys are first rounders. However, that means having to forego drafting Tavon Wilson in the third round, just as an example.
1. You draft Carlos Dunlap instead of Jermaine Cunningham in the 2010 draft at #53, and you draft Greg Hardy at #150 instead of a punter. Both guys were on my short list. You can never have enough good edge rushers, and punters can be found any time.
2. You draft Navorro Bowman at #63 in 2010 instead of a slow thumper like Brandon Spikes.
3. You draft Harrison Smith at #25 in 2012 instead of Dont'a Hightower, and Lavonte David at #48 instead of Tavon Wilson. Boths guys got extensive attention from the Pats. You want guys who can play in space.
3. You draft Muhammad Wilkerson at #28 in 2011. Another guy who the Pats looked at closely. Then, when Mark Ingram is still on the board, you trade #33 to New Orleans for #56 and a 2012 1st, possibly throwing something in as change.
4. You take Richard Sherman in the 3rd or 4th round in 2011. He was my day 3 binky that year.
5. You do a bit better with your FA signings, and pick up Terrance Knighton in FA this year, knowing that Wilfork can't last forever and needs to reduce his snaps.
Your defense:
DE: Greg Hardy, Carlos Dunlap, Chandler Jones, Rob Ninkovich, Michael Buchanan
DT: [Vince Wilfork -> IR], Muhammad Wilkerson, Terrance Knighton, Sealver Siliga, Chris Jones, [Armond Armstead -> IR]
LB: [Jerod Mayo -> IR], Navorro Bowman, Lavonte David, Jamie Collins, Dane Fletcher
S: Devin McCourty, Harrison Smith, Steve Gregory, Duron Harmon
CB: Richard Sherman, Aqib Talib, Afonzo Dennard, Logan Ryan, Kyle Arrington