So what? We're talking about events before the War of Northern Aggression. What happened afterward has no bearing on the concept of secession prior to TWONA....
Your claim was that no state would have joined the union if it thought it could not later secede; a third of the states joined with the explicit understanding that secession would be all but impossible, which tends to undercut that argument.
“No state would have ever” is somewhat hard to reconcile with the fact that seventeen states did.