Interesting discussion. I would say Yoda is both right and wrong. Size matters not in theory, and a Jedi completely in tune with the Force, reaching a complete state of enlightenment, should be able to move planets, and crush Death Stars. However, no such Jedi exist, or have ever existed. A Jedi has to work all his life to get more in tune with the Force, and the training never ends. Yoda is much more in tune with the Force than most other Jedi, but even he has not reached that asymptotic state, because you basically have to be immortal to reach it.