That was never the flaw and this definitely seems to be a classic case of misinformation within the fandom. Whis just stated that Blue can't be used in succession because the form heavily drains stamina while the Saiyans use it, not that "the act of transforming" itself consumes stamina. To the contrary, prior to its completion, transforming while attacking was the only method that actually allowed Goku or Vegeta to briefly use close to 100% of its power, provided that they didn't already lose a lot of stamina beforehand (which is precisely what happened in Vegeta's case because he already used the form against Cabba).EGonzo wrote:At first the flaw was that you couldn't transform over and over like the other transformations, because the act of transforming took a lot of stamina.
This is the same mechanic that was prevalent throughout the Future Trunks arc. It was always "Super Saiyan 3 on steroids" as you put it -- Goku even specifically explained that the switching-while-attacking trick Vegeta used against Black was the exact same trick he himself used to gain the upper hand against Hit.
Vegeta never uses Blue's full power against Beerus until he absorbs its energy to become the completed state. As established in the Future Trunks arc, they're not capable of using Blue's full strength unless they're able to transform while attacking or seal its power within their bodies. In other words, Blue's power starts to decrease pretty much immediately and gradually gets even lower over time.EGonzo wrote:Using normal Blue (right as he transforms, so he's logically still using the full power) he can't do anything to Beerus, but as soon as he goes Mastered he can actually land a punch on him.