Intelligent routing would presumably need to know and act on a lot of state across their cluster, and if that's got to flow through a single node, you can see h

Intelligent routing would presumably need to know and act on a lot of state across their cluster, and if that's got to flow through a single node, you can see how it would present a bottle-neck as the cluster size and requests per second increased. On the other hand, you can do randomised routing without knowing any state at all. You can do it with more than one routing node as well, which makes scaling almost trivial. I presume there are Hard Problems associated with partitioning a Heroku-style cluster for intelligent routing, or that's what they would have done.