As to whether arbitration agreements can defeat class claims, the answer is an emphatic yes. The defendants in several purported class-action race discrimination cases were able to defuse the cases by invoking arbitration agreements and getting rid of the class threat.
A couple of caveats are in order, though. The arbitration agreement must expressly state that there will be no class relief in arbitration, and the drafter has to be careful with the severability clause to make sure that if a court finds the class-action waiver to be unenforceable, the entire arbitration clause becomes unenforceable. The last place a defendant wants to be is in a class-action arbitration. At least in class-action litigation, court procedural rules provide a road map for the parties. Class arbitrations are pretty much unexplored territory, and defendants don't want to go there.
All that being said, there are pockets of judicial hostility (California, the 9th Circuit and others) where getting your arbitration agreement enforced can be a challenge. Even California courts, though, have stated in their decisions that some class waivers are enforceable.