Nowhere, then or later, did Lincoln agree that secession was legitimate, lawful or constitutional.
Why are you doing logical backflips to avoid stating the obvious? You are now trying to lie to yourself, and I can assure you you aren't being successful at foisting this nonsense off on me.
By what logical contortion can you argue that pulling troops out of Sumter is not a capitulation to the claim of sovereignty of the CSA? You are now in the ridiculous position of trying to argue that Lincoln was willing to give up control to an authority he refuses to recognize?
What you are doing is arguing a variation of the "no true Scotsman" fallacy. By saying that No man of principle would recognize the secession of South Carolina by giving up Ft. Sumter to them, so therefore what he was contemplating was not that, because Lincoln was a man of solid principle.
No, what he was contemplating was trading the principle for which he claimed to have been fighting that war, for the state of Virginia. A valuable prize no doubt, but not worth the abandonment of the asserted principle for which 600,000 people were made to die.
Stop trying to walk back what you revealed. The cat is out of the bag, the genie has left the bottle, Pandora's box has been opened, and you cannot now put the toothpaste back into the tube.
Lincoln was not against secession per se, he was against a secession that cost him sufficient power and influence.
Another thought occurs to me just now. If Lincoln was indeed an opportunist of little scruples, then what's to say he was willing to temporarily gave up Ft. Sumter just to keep Virginia in the Union, so that later when he decided to attack that "rump" confederacy, he had all the more power and forces to do so?
If one postulates that he is a man of little scruples, this scenario becomes all the more plausible.
I think I may be beginning to see the larger outline here. Promise them whatever you have to, (his willingness to cede slavery to them is but another example) but secure a strong position from which you can better impose your will later.
Machiavelli would be proud.