A cargo bike with an e-assist may cost you more to acquire than a used car, but it's probably going to pay for itself within the first year. Car insurance/gas/maintenance gets expensive, very fast. It sounds like you've already run the numbers, so good on you!
About the only downside to a car, relative to the setup you test-rode, is dealing with rain. Your city seems to be bike-friendly enough that it shouldn't be a problem finding rain-friendly clothes, and taking routes where cars won't splash you. You can even take a passenger or two on a Bullitt, right?
(Personally - if I lived in such a bike-friendly city, I'd prefer to spend a few minutes drying myself / changing clothes after rain, than spend thousands of dollars a year maintaining a car...)