It shows a lack of familiarity with the tooling. It's actually quicker to write something that prototypes the model you're testing -- as little as a few lines of code -- that eventually saves a lot of repetition.

That prototyping later becomes extremely useful for building local databases -- a strong factory suite means I can rebuild my local database and have it completely populated with randomized dummy data. Changing locales on some packages means I can have a local environment populated with data tailored for a completely different country and language, for example.

Re: surfacing bugs -- in a lot of cases yes. And a lot of bugs have been found this way.