The point is, if the federal government had tried to restrict private ownership of certain kinds of artillery in the early 19th century, would it have been held to have violated the 2nd? Nobody can say for sure, because the issue (to my knowledge) never came up – but if it did, I expect SCOTUS would have drawn a legal distinction between small arms commonly used for infantry, hunting and personal self-defense, versus larger scale military weapons. Such a distinction can be defended on originalist grounds, since small arms was the primary thing the people who voted for the 2nd were thinking about.

It actually raises an interesting historical question – to which I don't know the answer – in the debates on the proposal and ratification of the 2nd, was the status of larger scale weapons under it ever raised?

You could own a fleet of ships all outfitted with many cannons