In the CFP Semi Final games - where they "best" are playing the "best", both with plenty of time off before the games:
SEC teams are 10-1 (6 of the 10 winners went on to win the title game. Twice they played other SEC teams - so 2 of the 4 SEC losses in the finals were to other SEC teams)
The last SEC team to lose a semifinal game was in 2014 - when OSU beat Alabama, in the first "Final 4" (Since then, they are 10-0).
B10 teams are 2-6 (1 won the title game, 1 lost)
The SEC teams aren't more successful because they only play 8 conference games. When their top teams play other top teams (and often it is both the top team, and the runner-up, from the SEC) they overwhelmingly win.
That is how they earned the reputation as the best.
FWIW, the other conferences:
ACC 4-3 in semifinals (all Clemson as the winners - who then went 2-2 in the finals)
Big 12 1-4 in semifinals (the one winner, TCU, lost in the finals)
PAC 12 1-1 in semifinals (the one winner, Oregon, lost in the finals)
It’s like having an extra week off. C’mon.