I most certainly do think that. And so did the US Supreme Court in Miller. They didn't consider what state Miller was from and read the Constitution of that state.
The concept is that of securing a free state. It applies to any government. Do you think that the security of a free territory, pre-statehood, is somehow achieved without a well-regulated militia?
You seem to equate lack of protection to lack of necessity. The Ninth Circuit's decision in Silveira didn't suddenly make the necessity of a well-regulated militia disappear for Kalifornia. The necessity wasn't created by the Constitution any more than the right to keep and bear arms was created by the Second Amendment.
Governments are instituted among men and derive their just powers from the consent of the governed. How can a territory adopt a constitution and become a state of the union without some appreciation for the rights of man. First comes the consent. Then the derived powers. The consent cannot be given by a disarmed people.
That militia disappeared long before Silveira showed up.
If California had a decent state constitution that protected the RKBA, Silveira wouldn't need to seek second amendment protection from the federal government. His own state constitution would protect his rights.
The citizens of California have spoken. So be it.