Let's be clear, Notre Dame did not play anyone from the SEC until last night. Saying they could beat everyone except Alabama, who lost to Texas A&M (so much for no other SEC team beating Alabama), is speculation at best.
Let's look at their schedule. They blew out Navy and Wake Forest. They beat an overrated USC team that got stomped on in its bowl game and finished 7-6. Their quality wins against top 25 teams: Mich. St. (squeaked by TCU in its bowl), Michigan (lost to SEC), Stanford (won the Rose Bowl), and Oklahoma (got blown out in its bowl by Texas A&M). Purdue got blown out in its bowl game and finished 6-7. They needed 3 OTs to beat Pitt, and they finished 6-7 and got blown out by Ole Miss. Miami, BC, BYU? Those teams would've been akin to Kentucky in the SEC.
PS: Saying they'd have finished 8th or 9th in the SEC is saying that they might be able to beat some SEC schools. There are 12 schools in the SEC. To be a top SEC team, they'd have to run through not just the 2012 Alabama team but Texas A&M, Georgia, South Carolina, Florida, LSU, and Vandy. All of those teams would have beaten the Notre Dame effort displayed last night. Which is what I said before.