Superman's heat vision was able to make stars go nova or even super-nova, depending on the type/size star. His super-breath was able to "blow out" stars. Those powers were said to be minor compared to his strength. It did seem to take all of his strength to move the earth. However he was able to move bigger planets with greater ease. Of course it always seemed like he was keeping power levels in check when he was on earth. Over time his "holding back" reflex probably became automatic. Thus moving earth would seem to take all his strength. To do it he had fight his own inhibitions & holding back reflex.
I question the first parts of your statement---or rather, would appreciate you citing a source. I've never known Superman's heat vision to ignite anything but an already artificial star, whose rules for working might be different from what we know. Nor do I remember him ever blowing out a star. (I do remember one story where Superman's powers were amplified by a near-omnipotent alien, where he was AFRAID something like that might happen.) I do remember Superboy moving a group of planets, threaded like beads on a string, but of course it depends on their size---several planets as small as the Moon or even Mars would be relatively easy to move for a being who can move the Earth with all his strength.)
I'm not, of course, saying you're wrong. Would just appreciate you citing a source. Also the "moving bigger planets"---I can't recall a time when he moved a planet where he mentioned, specfically, it was bigger than Earth.
Thanks!---Al