I think the reason we don’t see higher keys is that, at that level, Paladin just does more damage and has more utility. Brew needs a bit more babysitting than a prot war, and it doesn’t scale in dmg with larger pulls.
Also, at those higher keys the pulls become insane in order to make time. We’re talking like 5 pack pulls that only a prot war/prot pally with CD’s rotating can pull off. Brew just doesn’t have the CD’s or the sustained damage reduction to do those large pulls. At best, we can do 20% DR with fort brew for 15s and about 45-50% for 8s with dampen harm. Once thats over we’re cooked, and packs are usually alive for a lot longer than 20s.