With my rubber trees (I have grown many dozen of them over several decades), I know when it/they need re-potting when their roots begin to grow out of the drainage holes. I don't really worry about over-potting them tough, I always use extremely well-draining potting mix. Carter, you are absolutely right. Always use pots that don't have a smaller diameter in the upper 1/3 than it does in the lower 2/3. Like you, I found out the hard way.
Rubber trees will actually grow quite well being root-bound (not that I ascribe to doing that
) but you'll have to water quite frequently. Being mostly roots, that remaining potting mix really does dry out very quickly. That alone is a good reason to re-pot. I re-pot mine twice a year. By the way, all of my rubber trees are rooted cuttings.