No, we have migrated prototypes to redshift. You just need to keep your database logic in a separate layer, which is something one should do anyway. I say "I think" because I agree with you that most will not. If you implement mongo such that you will be stuck on mongo, then do not use it. You always want to have a layer that handles your database operations, with any database, but obviously you are safer in SQL-land as switching costs are lower.

I do not think the "cancer" metaphor is valuable here. What you describe are bad ideas that I agree are bad ideas but really one has to know the tool they are using and what it is bad at.

I think the thing you describe can happen but that is just poor planning more than anything. Why does the database have anything to do with the design of your API layer? That sounds bonkers. And I would not blame the underlying database tech. I would blame the implementer.

But really, please consider that many of us have, or are as we speak, losing loved ones to a deadly sickness which you have compared to a poor database implementation.