Absolutely correct about exceptions. We've had 9 dachshunds in total over the last 13 years and I wouldn't attempt to predict bidability without seeing a pedigree and even then, as said, individual variation occurs.
Personally, I don't know any that stalk to heel perfectly, off lead, in any circumstance and any degree of natural distraction. That's not to say they don't exist - but I wouldn't recommend it as 'the norm' to a prospective owner. There are lots of things that they are brilliant at - imho walking at heel, off lead in a hunting environment isn't one of them.