I don't see growing root mass as necessarily competing with growing flower mass. The roots are the nutrient channels, the mouths and stomachs if you will. So more mouths and stomachs seems to mean more of anything and everything the plant can do, right? Post-transplant is a special case though, the plant has to get itself situated, so to speak.
I've been saying for a while that the plant continues to grow root mass after flowering has begun, too. :p