Actually I wish they had done it in an even better controlled more targeted manner. Something like:
Phase 1: only TEC
Phase 2: only advent
Phase 3: only vasari
Phase 4.1(shorter phase): TEC & Advent only
Phase 4.2(shorter phase): TEC & Vasari only
Phase 4.3(shorter phase, but a bit longer then 4.1 & 4.2 as this matchup has always been complicated): Advent & Vasari only
Phase 5: All races enabled.
The point is I think the devs had a good idea: they are essentially doubling the number of factions, so restricting gameplay to less factions at a time initially allows for better balancing of the rebels against the loyals of each respective faction. Like I said I wish they had gone even farther to focus on one matchup at a time. It's really a much more efficient way of balancing as compared to having all races enabled.
As it stands even with 2 races enabled we're already starting to produces a confusing mess of unrelated feedback on the beta feedback forum. When everyone is talking about a single faction it's easy for the devs to browse the forums to get a general consensus on that faction. By comparison the current state of things, some threads pertain to the advent, some pertain to the TEC, and some pertain to the advent VS TEC matchup. Combined with the wide variety of opinions and the inevitable incorrect views some testers will inevitably hold, the congestion caused by having feedback related to multiple races on the forums is likely making it much harder to sort out the good well reasoned feedback on a given topic from the less substantiated feedback.
Actually, in the current state of things it would be great if they'd give us a few subforums for feedback related to the different races. That would organize feedback a bit.