Your example is not the good one. Because in the 2 case, you'll lose 3 Diamonds, with Xp in the one, Circuit + Iron in the other. The problem that could be mentionned would be the fact you need Diamond to repair Vanilla Pickaxe, while you only use Energy for Rockcutter. But I'm not complaining about the Rockcutter, since it's speedness is already a problem --> I only use it on Diamonds, Uranium and if never I find one, Iridium. But I agree with the fact it should be a little more expensive (than Diamond Pickaxe). An energy Crystal instead of the RE-battery would be enough, + non being compatible with Batpack.
Edit: You're cheating, you've edited your post 5 times and it makes the mine a bit irrelevant. When I did it myself, that was for grammar corrections.
sorry, but when I read your post I realize that my translation was not accurate and my post was confusing my original idea.