Oftentimes better understanding of the problem needs trying out solutions. Armchair architectures tend to blow up in contact with reality.

For sure, though with databases it's usually pretty clear even at the start whether your "objects" will be relational in nature. I can't think of a single time that hasn't been the case, over hundreds of apps/services I've been part of. Things like asynchronous jobs, message queues, even object storage, I fully agree though.

Even a JSON column would be better in most cases IMO, and on Postgres you can also make indexes on json keys.