I am literally in the middle of swapping DynamoDB for a RDBMS.
The idea that you can abstract away such fundamentally different data stores is silly. While I hate doing it now, reworking the code to use relational models properly makes for a better product later.
I see. It seems like you may be one of the people that try to coerce relational models into nosql stores like Dynamo.
Or course it's possible. They even trick you into thinking it's a good pattern by naming things "tables".
But if you're using Dynamo to its fullest an ORM is not going to be able to replicate that into a relational store without some fundamental changes.