Ok, I admit my comment is a little overboard.

Comparing Mysql migration to Postgres is not really helping this discussion. Postgres has transaction DDL with many schema change operations being O(1).

Most of the time your data has structure. Only parts of it are usually semi-structured. And yeah, I had this problem too, until I automated it and don't have it anymore. So I guess I'm a little annoyed when I see that schema change automation didn't really took off and people accepted JSON as a storage medium.