This had nothing to do with the Supreme Court being corporatist.

The problem here is simple: Congress passed a law making mandatory individual arbitration clauses/etc clauses in contracts legal. The supreme court simply said "yeah, they can do that".

Your real problem here is with Congress passing dumb laws, not a "corporatist" Supreme Court.

I'll also point out that the Supreme Court were the ones who created/imported representative litigation into the US in the first place, and the ones who started to interpret the federal rules of civil procedure in a manner that allowed representative litigation like class actions.