Are you really that dumb? Did it ever occur to you that with the supermajority required by your thesis, you could have any policy you wanted? Why in the Hell would you secede if you could dictate to the minority any policy you wanted?
Nutty as it is, let's try out your theory: because of the difficulty in amending the Constitution, a situation could develop where 74% of the states wanted to secede, but the remaining 26% opposed it. Nobody in their right mind in the ratifying conventions would have voted to surrender that much sovereignty. Such a surrender would be not only to the Federal government, but to the whim of a small minority of other state legislatures. They were in their right minds, unlike your analysis.
All attempts to agrue secession as Constitutionally prohibited ultimately come down to needing Lincoln's hallucination that the Union preceded the Constitution. All else is window dressing.
Actually, the secession issue did need a Constitutional amendment. An amendment to prohibit it.