I'm with the product team at Prisma, currently focusing on migrations.
You are right about the fact that declarative migrations introduces some design challenges that can be hard to solve. In the current version of Prisma Migrate, changes to the declarative schema file are translated to auto-generate incremental migration files.
We have a few ideas for how we can improve our system to better deal with these challenges. Please feel free to follow along or check back in a few months if you are interested in how we solve (or not?) these problems! :)
You're modifying existing state so it has to be incremental.
I'm curious to see how Prisma plans to handle these real-world use-cases.