The claim that good schools are good because of small class sizes and higher teacher pay, that it is as simple as that and that there is "really no debate" is false. Pointing out that A and B are not the only factors, it's not as simple as that, that there is plenty of debate, and describing an additional factor beyond just A & B is not "dismissing" A and B.
Consider the scenario I described: a large school district with multiple neighborhoods where the admin, funding, class sizes, teacher pay, etc., are the same but the student bodies differ. You might be able to equalize outcomes by giving the lower-performing school smaller classes and better-paid teachers, or you might not, but even if you did, you would then have to explain why a school with smaller classes and better-paid teachers wasn't doing any better than one without those features. The answer would remain the same: because there are other factors that matter, too. It's not as simple as just smaller classes and better pay for teachers, and there is plenty of debate about what factors matter and how much.
There is plenty of debate about what makes for good schools. Many school districts are large enough to include neighborhoods on "both sides of the tracks". It is the same school district with the same pay, same class sizes, same teacher demographics, but different student body demographics. Result is often a large disparity in outcomes for students. In one school, a student who wants to succeed has to compete with his classmates who want the same thing. In another, the same student would be abused by classmates for trying to succeed. Parents in these latter districts will often make huge efforts to pretend to be living a few miles away to give their children not smaller classes or different teachers but different classmates.