One Question you failed to ask, which i believe is the most evident question that proves OSAS can't possibly be True is:
If once you are Saved, your name is written in the Book of Life and can't never be removed, why are there Scriptures which plainly teach a persons name can be removed from the Book of Life?
The mere fact that Scriptures teach a name once written in the Book of Life, can be blotted out of it. is ABSOLUTE PROOF, that Once Saved Always Saved, can't possibly be True.
Same line of questioning would be. Is it True once you are SAVED, your name is written in the Book of Life? Most know the answer to be TRUE. Then ask those who believe OSAS to explain how a person is blotted out of the Book of Life, ask them "Wasn't that persons name written in the Book prior, wasn't that person SAVED, thereby being written in the Book of Life, how then are they now blotted out of it?
People have been wearing those blinders for so long, they don't know the Truth, nor are they willing to learn the Truth, they are so use to the blinders.
Responding to OP