> If you at all bother to understand your problem domain

This is a startup. There is no problem domain. There is no spec. There's none for a startup. You may not even have code.

If you're doing a "startup" but have this ironed out, great, everything you said then applies, but it's not a startup, since you found your business model, it's a small company.

And I would love to enforce constraints on the DB but unfortunately, I already had "primary keys" that repeat, unbeknownst to the project customers.