Sounds like the definition of random to me.

I expect that the distribution is even and that each weapon has the same chance to appear. One showing up more than others, though, is just the luck of the draw.

It would be nice to see the totem drops again, so that you can at least try to work on one via slow progress (it could be a chance drop at ~50% and follow the need/greed system). It was the most frustrating thing to do many runs and not see your weapon. Knowing that you can have a shot at progressing to it, though, is always a nice alternative.