The 300A and 300B RCs both have the same power output for the control signal. It's only the 300C version of the RC that has reduced power. If you don't do any very long range flights, you probably wouldn't notice a difference with any of the versions in that regard.
The A has the
DaVinci processor and USB 2.0. B and C don't have the internal video processor, but have USB 3.0.
The video transmitter is in the bird, and the power for that has been reduced with each new version of the Phantom. First reduced by 18% in relation to the original and then later by 30% in relation to the original.
Old Motors vs. New Ones