I think a good measure of true conference strength are overall NT wins.
Once you get to the NT there basically is no way to hide or inflate records & rpi by scheduling 80% of the non-conf against sims.
And once you start getting around 20 NT wins in a single season you're approaching dominance. The Allen-Calif between seasons 79-81 went 20, 20 & 21 NT wins. 61 over three seasons is very impressive.
The most dominant three year stretch I've seen at D2 (there may have been better) was Allen-Gulf South between seasons 57-59, having 22, 24 and 23 NT wins for a three season total of 69 NT wins.