Followup: on another playthrough, I got three enemies on a single trip to the market (not good at all!), but then again I made it to Epoch 4 (much better!).
The other thing that struck me was that, when the epoch changes, you don't get a chance to go to the market--and in particular you don't get a chance to use a banishment power. Sometimes that felt frustrating, but if it's a deliberate choice in the design, I can imagine why.