It takes only 50 votes to rule a filibuster out of order. And none of the seven took the "nuclear option" off the table if the Democrats tried to filibuster. In fact, only two need to vote for the nuclear option, and four explicitly backed it. As did one Democrat. So that's 53 certain votes.
If they had 53 certain votes then why didn't they simply have the vote? You're writing about not trusting the President's judgment but you take the gang of 7's word? If they were serious about the issue they would have addressed it right then...instead they created a little gang in the middle to sign off on the President's nominees and keep the civility of their club intact.