I disagree. They never looked. Dontario Poe was the first +320 I remember signed as a FA. The Landry Flex, Jimmy Johnson Attack 4-3, Parcells 3-4, Phillips 3-4, and Tampa 2 never called for big +320 pound DTs.
If that is what you want, fat tree trunk guys, they are not hard to find. Remember Vince Wolfork, Shaun Rodgers, Poe, were a freak athletes that just happen to be +320. Remember Ratliff, Hatcher, Canty, and Spears were all 285-310 on 6-4 to 6-6 frames out of College. Tony Casillas and Chad Hennings were not +320 pound run stoppers.
Name me the +320 DT on the Legion of Boom? Nobody, closest was Red Bryant and he was a freak athlete 6-4-318 pounds running a 4.90 40yd time.