A bunch of schools, not just Clemson, have replaced Tennessee.
During the 1995-2001 glory years the SEC was a two-team conference. Florida and Tennessee. In the Southeastern part of the country, Spurrier, Bowden, and Butch Davis fought over the Florida talent and the rest of it went to Tennessee. South Carolina and Clemson were terrible. Georgia was mediocre and inconsistent. Alabama was inconsistent and on/off probation. Auburn did have some good years but was also fairly inconsistent. LSU was awful.
Look at what each of those schools has experienced from about 2005 until the present. South Carolina had a distinct up period with multiple 10+ win seasons and a division title. Clemson won a national title, played for another, and routinely wins conference titles. Georgia consistently won 9-10 games, occasionally won the East, and won the SEC/almost won a title last year. Alabama is experiencing the greatest run by a team in the history of the sport with 5 national titles. Auburn and LSU each won a title, played for another, and won the SEC twice. Each of those schools I just mentioned did nothing even close to that from 1995-2001. When you stop and think about it, it is staggering how much better the conference has been over the last decade than it was in the 1990s. It is painful to admit, but when the rest of the conference got better, Tennessee just completely disappeared from the stage. During the SEC's glory years, we were completely MIA.
Think about key players we had during that era and where they were from: Peyton Manning, Jamal Lewis, Peerless Price, Tee Martin, Shaun Ellis, Travis Henry, Raynoch Thompson, Deon Grant, Cosey Coleman, Albert Haynesworth, etc. Each of those guys went to high school in an area located firmly in enemy territory, whether it be LSU, Georgia, Ohio St, Alabama/Auburn, South Carolina/Clemson, etc. A bunch of those guys, if they were top high school recruits today, probably don't come to Tennessee. We still might catch a John Henderson, an Eddie Moore, a Jason Witten, a Chad Clifton since they were in-state, or maybe a Donte Stallworth since he was from California, but we'd get nowhere near the same volume and depth we got in the glory days. Tennessee is at its best when we are able to recruit nationally.