Again, moving Celestial objects is a different kind of magic. It doesn't matter if she moved the sun or not, the point is that the power put into moving celestial objects doesn't translate into the same force used to move terrestrial objects, or else defeating Tirek would have been a walk in the park. All they would have had to do is spear him with a few mountains...
Twilight had all three of the Princess's powers and she still had trouble defeating Tirek, but did you ever see her uproot mountains with her power? She could punch holes through them, maybe even blast them to bits, but if you cut that power down to 3/4ths, do you really see Luna picking up Canterlot?
The power to move celestial bodies does not translate to moving terrestrial objects.
However, I will grant that teleport would be an effective move to put Jigglypuff out of play, if it wasn't for the fact that Jigglypuff can use copycat, so she could teleport herself right out of anyplace Luna puts her.