You are also missing the point and in the same way.

You are at A, you want to go to C. We are debating which B to pick between:

1. a filesystem + implementing library over that to cover the interface between A and C.

2. Postgres (which is the same as above - just not invented here)

Now, both of you are imagining a world where #2 somehow implies more complexity and also more second order effects than #1 would.

Nobody uses all of Postgres, but the cost of not using more than 1% of what's available is hardly larger than implementing that 1% yourself for most use cases. And please don't make the misstake of thinking that I'm trying to sell Postgres over any other database product - this is all to do with the worse is better idea that so many of you cultivate.