Goku can still be "just" a planetbuster if Frieza was too. Planets are of different masses. The strongest "planetbuster" would be able to produce roughly 100,000,000 X the amount of joules that the weakest "planetbuster" would be able too.
How is it not PIS when he survived being surround by celestial objects whose gravity would destroy the Earth while sleeping?
The Elder Dragon is limited against those whom are more powerful then he. Otherwise they could have just wished Cell/Buu away. And even if that was the case they would still have to make the wish before they were frozen in time and considering they are bloodlusted it's unlikely they would/