Well keep in mind for comparing relative SOS that A&M and OU each played Texas, while Texas was dragged down by playing A&M and OU. Just saying. 
Also, if you're going to attempt to compare the relative W/L opponent record like this...
- Texas' SEC opponents went 24-40, Oklahoma's went 40-24
...then you are going to need to remove the games played against Texas, and OU, respectively. Because Texas delivered 7 of those losses to its opponents, while OU gifted 6 of those wins to its opponents.
Actual valid records for relative comparison are 23-33, 34-22. There's still a sizeable delta, but it's not quite the same.
This is definitely a fair point, I'm just not doing it because it is a tremendous amount of work.
Also, yes, Texas' schedule IS easier because they didn't have to play Texas. Same goes for:
I used to say that jokingly about Alabama. But of course, you can't penalize the best for being the best.
Ohio State's record is always good because it doesn't have to play Ohio State.
If you look at the SEC teams, most of the winning teams' opponents had a sub .500 record and most of the losing teams' opponents had a winning record. That is just math.
If you are Mississippi State and you went 0-8 then there are 15 SEC teams that you could potentially play and the cumulative record of those 15 teams is 64-56 so, on average, your SEC opponents are going to be .500+ and for Mississippi State they were, 41-23. Conversely if you are Texas and you went 7-1 then there are 15 SEC teams that you could potentially play and the cumulative record of those 15 teams is 57-63 so, on average, your SEC opponents are going to be <.500 and for Texas they were, 24-40.
I think what probably matters more is the # of games against CFP teams and the # of games against .500+ teams. Texas still gets kinda screwed there by being good because there were only three CFP teams and since Texas was one of them, they could only possibly have played two. Similarly, there were eight .500+ teams but since Texas was one of them they could only possibly have played seven.
Texas played one CFP team (UGA) and three .500+ teams (UGA, UF, aTm). Oklahoma played two CFP teams (TX, TN) and SEVEN .500+ teams. That is the part that is nuts. Only one of Oklahoma's SEC opponents finished below .500. That is a LOT of tough games.
Sure, part of it is that Oklahoma had to play Texas which was .500+ and CFP while Texas got to play Oklahoma which went 2-6 but even if you just toss that game out, in Texas' other seven SEC games they played 1 CFP team (UGA) and three .500+ teams (UGA, UF, aTm). In Oklahoma's other seven SEC games they still played a CFP team (TN) and six .500+ teams.