I’m not really sure how you get “perpetual” or even “enduring” out of “more perfect,” frankly.
Like I said, given that the Articles of Confederation were explicitly perpetual (but if it were indeed perpetual, as it claimed, query as to how it was eventually dissolved; after all, if it was perpetual, how come we aren’t governed by the Articles of the Confederation? And, moreover, how can a parliament bind future parliaments?), shouldn’t it have been easy to include similar language in the Constitution?
The notion that the Union was not perpetual did not even occur to anyone until the 1830s, when pro-slavery politicians invented a supposed constitutional right of a state to secede.