You should read Grantley McDonald's paper on this question. On these points he is fairly good.The point was that the Comma was not in ANY Greek manuscript, not even Vaticanus. Erasmus refused to insert it into his TR without Greek manuscript support. That's why Erasmus' opponents had to dishonestly create a counterfeit manuscript, "Codex Montfortianus", just to present a Greek manuscript that allegedly had the Comma. Of course, Erasmus knew that it was a fake, but he kept his word and added the Common to his TR based on the bogus manuscript. And yes, I know KJV-Only's are going to claim these are "false facts", because they HAVE to.
And you are jumping around, I just explained to you why his correspondence with Bombasius included the heavenly witnesses.