Jackson Arnold had looked terrible against Houston and Tulane as well. Granted, they might have been in a better spot sticking with him long-term at this point.
Oklahoma's real issue is its offensive line. Everyone mentioned it all off season but Sooner fans and, in some ways, the program at large stuck their heads in the sand and now they are paying the price. This isn't the Big12 anymore.
I think people write off SEC and B1G sometimes because they lay eggs in OOC games like Auburn vs. Cal or Arkansas vs. Oklahoma State this year but the SEC truly is a better league than the Big12 and it was a jump. OOC games are just not treated with the same intensity as conference games for the most part (well unless you are Big12/Pac12 wanting to get respect and you treat every SEC opponent like a superbowl game).