Freiza was able to destroy Planet Vegeta whilst in his powered down form, way before the reached the power that Goku was matching before he went Super Saiyan. He should be able to destroy stars, hence solar systems, at Super Saiyan. Super Saiyan 2 should have no problem defeating Superman if one doubts SS1. SS3 you could argue should be able to keep up with a solar powered Superman, but not being able to defeat Superman at SS4? Come on that's just nuts.