I would like to think that the built-in UBEC wasn't the only thing holding it back! Switchers are actually quite simple really, and should be fairly easy to replace the linear BEC. No, I would think the problems stem more from the programming aspect and trying to get it to work with all motors (noteably slotted stator types).
The guys at CC might simply not know what the ESCs are capable of. I hooked up a Plettenberg Extreme on a MM and it is working great. Really smooth and it only got warm after about 15 minutes. In Plettenberg's website states they are built with 4 and 6 poles. I don't know what pole the Extreme motor has, but it is a great motor. I only used 7.4 volts and I'll try 11.1 volts some other time to see if it can handle it.