I used 1992 because Tennessee didn't play Florida and Georgia every year until then. And it's been a problem. Doesn't mean it's a problem that can't be overcome. It has been overcome.
But, Tennessee has beaten Florida, Georgia, and Alabama in the same season twice since 1992 (1998 and 2004). While Tennessee has been "down" that also includes Tennessee's "Decade of Dominance". So, I would say schedule difficulty is a factor.
The argument centers around the potential of two theories. 1. Tennessees difficulties during this period of time (conference expansion) are part of a cycle and purely coincidental. Or (2) the new landscape of college football has been a cause of Tennessees problems.
I think it is coincidence. But, I also think it was a lot easier to win in 1981 than it is today. But, thats true for everybody.
I disagree with this. It's actually a lot easier for SEC teams to win today than it was back in the 90's and 00's.
Here's the thing: SEC teams were punished in the 90's and 00's for having difficult schedules. A classic example is 2002 Georgia. They went 13-1, beat five top 25 teams, and were completely dominant at the end of the season, but got left out of the national title game because Miami and Ohio State ran through soft schedules undefeated. There's a good chance that Georgia would've won the national title that year if there had been a 4-team playoff. Indeed, the toughest competition was likely #4 USC at 10-2, not Miami or Ohio State (the eventual national champion).
Or how about this: Florida may have won a 3rd national title in the 00's with a 4-team playoff. The 2001 Florida team that got upset by Tennessee was probably the best team in the nation that year. Essentially, the top teams in the SEC beat each other that year, but those top teams were all dominant in their bowl games. Meanwhile, Miami got one of the easiest (and most controversial) national title games ever with Nebraska, which had just been clobbered by Colorado. While it's not clear which 4 teams had made the playoff (since they used computer formulas back then rather than a committee), it's possible that Florida would've been the #4 seed in the playoff and won the title.
Even the 1998 Tennessee team would not have won the national title if it weren't for the "stumble and fumble." Yet, it seems clear in hindsight, that Tennessee was the best team that year, particularly with the win versus Florida State. Very possible that Ohio State or Kansas State plays in the national title game if Tennessee loses a close game to Arkansas.
Let's not forget about undefeated 2004 Auburn that was left out of the national title game. Would they have beaten USC? I'm not sure, but certainly they would've performed better than Oklahoma did in the title game.
It's easier for SEC teams to win the title in the playoff era, because now they aren't punished for playing a brutal conference schedule to the extent they were back in the 90's and 00's. Saban doesn't win in 2017 under the old system. He was actually ridiculously fortunate to have won in 2011; a mere 6 years earlier, there's no way the pollsters would have passed up on Stanford or OK State as LSU's opponents in the national title game. The SEC did not start getting the 'benefit of the doubt' really until 2007 after Florida crushed Ohio State in the national title game.
There are 7 SEC powers (Bama, UGA, Florida, Tenn, A&M, Auburn, LSU). The 1 team out of 7 that is the best of the group always has a reasonable shot at the national title now. That wasn't the case in 2005 or 1999. Also add in the fact that the SEC is in the most talent rich portion of the country for recruiting purposes and the SEC schools tend to have the most resources, and I'd say that any of the SEC powers have a better shot at national titles now than they used to. SEC teams no longer have to go undefeated to compete for the title. Now they can lose 2 games and still get in so long as they have strong quality wins.