Earlier quoted context omitted.
I currently just use regular Rails migrations for this. In fact, I've executed each of the examples you provided using database migrations. You mentioned not wanting to use the console or a one-off script, but why would I want to switch over to SeedMigrations from regular ActiveRecord migrations?
Another one of the engineers here. While using ActiveRecord migrations will work for production systems, when setting up development or test systems using rake db:schema:load will not actually insert those records. Since rake db:schema:load is simply loading the current schema from schema.rb, you will still have to add those records into seeds.
Ah, interesting, thanks for the explanation - I was wondering the same thing as your parent. I always do db:migrate instead of db:schema:load, but I can see the advantages of avoiding that (particularly if you have tons and tons of migrations).