What if a province stays allied for years - do we force it to become a roman province eventually? What is the problem with letting the player choose when to destroy the type3 or type4 and then build a type2 in its place? AI won't do it, but then AI never gets a type4 anyway - the scripts automatically place the best type for them when they take it.
Because in the time it takes to rebuild the type 2, they are without any recruitment, population growth bonusses and law bonusses.
There would be nothing forcing them to upgrade, but it saves building complexes and prevents problems like the one above