Is it true that most big tech companies and possibly the startups you work with strongly prefer H-1B transfers over candidates who might have held an H-1B in the past (with an approved I-140), but are currently on a B-2? In your experience/opinion, is such a situation disadvantageous to the candidate's competitiveness in attaining employment at these coveted companies?

If the company is paying attention and knows what it's doing, then the interim B-2 status of a candidate shouldn't matter; at worst, it just means that the candidate might have to depart and reenter to activate his or her H-1B status with the new employer.