I figure any ship in the FS universe capable of destroying a planet do it one of two ways.
1) Orbital bombardment devestates the surface and results in nuclear winter from the resulting dust cloud - in addition to bombing any population back to the stone age. THe result is that a once habitable world turns out somehing like
Lucifer falls in the high end of this catagry IMHO
2) Bombardment results in massive tectonic upheaval and Basically reduce the surface to molten slag - think devestated Earth from BP:AoA
To fair in canon, the Sathanas did detonate a star wiping out a Star System, but that took a fleet of them. I figure a single Sath belongs in the lvl2 catagry of planitary destruction Though i imagine a Sath fleet could do something nasty to a planet. the Gargant and Vinashaak also occupy lvl2 - even though they are non-canon
Now before people start throwing Star Wars at me, let me paraphrase a well known net saying - "They did it on Star Wars" should never be an allowable rationel for anything. Ever. Not even breathing.
Besides ships in star wars were rediculously overpowered. Star Trek ships as well. but it is a moot point as these are all seperate universes anyway. so using them as an argument is dumb.