It's not clear if it was entangled because it was written in the specific framework or because it was just badly written code. In the latter case, this hasn't really anything to do with the framework. Additionally: did you make the v0.12 a migration just work, or did you change the codebase to take advantage of the new features (and remove inherent duplication)?

There are inherent problems in the TF framework and the migraitons. 0.12 introduced for loops, and 0.13 added modules support to them. So a proper migration should convert deduplicate resources into lists of resources. This is painful for big models, since one needs to write scripts in order to convert resource associations in the statefile. And hope not to miss anything!

Due to the strictly declarative nature, it's also difficult to slowly move duplicated resources into lists, and handle both of them at the same time.

At this time, our time is stuck with a certain TF version, and can't move without spending considerable resources.