There is an entropic force that leads most organizations to optimize for survival of the organization over time, and worsen the ability to serve the ostensible purpose the organization exists to serve. Changing the type of the organization doesn't matter much if this tendency is not addressed honestly in the mission statement or somewhere similar.
I was totally with you until you proposed that a careful mission statement is the solution to organizational ossification. I've always considered them a symptom, and to the extent that they are prescriptive, you can safely assume that the operational reality is the polar opposite.
I said "honest" not "careful", but really it's about actual intentions, not paper promises. It's just a label for intentions, and as you point out, manipulated to hide intentions more than describe them.
