Please keep the conversation civil and on topic.
I think it is correct to say that the Landmark Baptists eventually forced Whitsitt out.
His arguments with Baptist orthodoxy were, as the book shows, secret, confided almost entirely to his diary; his colleagues — and adversaries, who would gladly have used them as ammunition against him had they known of them — didn't know of them. It was his insistence that Baptists recovered immersion in the mid 17th century that landed him in hot water, as can be shown by a reading of the various associational and state resolutions calling for his ouster.
However, the controversy over his findings are of a piece with the personality Bro. Robert has outlined in his blog. A.H. Newman, for example, generally agreed with Whitsitt's thesis, but criticized Whitsitt for espousing the thesis (anonymously) in a journal often hostile to Baptists.