None of this attempt at apologia works.
The Northern dominated Congress and the Lincoln administration supported slavery effectively forever by express constitutional amendment. Lincoln endorsed it in his inaugural address. If anybody had any question as to whether secession or the war were “about” slavery, that fact answers it decisively. It was not. The North was quite prepared to accept slavery.
The original 7 seceding states on the other hand, rejected protections of slavery that would have been impossible to overturn for many generations (including right down to the present day). Instead they opted for independence.
Looking at those facts, one can only conclude it was not “about” slavery.
The Vice President of the CSA said the CW was about Slavery.