If Biglaw or Midlaw is your goal, it's stupid not to consider ranking. Should it be considered above location or cost? No. But many employers do care about it.
Yes, I completely agree. Especially at big firms, prestige and national rank matter greatly. As you've shown, most attorneys at big firms went to prestigious law schools, and they like to hire from peer institutions.
In the handful of cases where someone is hired from a non-prestigious school, however, I wonder how much the rank of their law school really mattered.
For example, if Gibson Dunn, a huge firm, has only a handful of lawyers from non-elite schools, then I have to think that school rank had very little to do with those people getting hired. Someone like that gets hired based on other strengths. They'd have to compete against T14 grads with impress pedigrees, which leads me to believe that they have uniquely stellar resumes, both academically and professionally. Maybe they were valedictorians, federal clerks, or have graduate STEM degrees.
Those people are so few in number that I don't know if the general rules apply. I think you can say that in the context of big firms in LA/NYC a non-elite law school grad overcomes their lack of pedigree, and gets hired despite the snootiness.
I went to a T3 in CA, and our top grads scored biglaw jobs. Even though the school isn't prestigious, the local biglaw firms have dealt with enough grads to know that the top grads are a good investment. I suspect that's the same in most cities.