The strength of graveyard creatures are different from that of the forest. Notice that they do not have levels, & their levels are simply displayed as "Undead"? The level which I created them in, determines how strong that creature will be in the graveyard.
Let's say if a graveyard creature's stat is based on yours and the level difference between you & the creature will increase or lover its stat by 0.1. That wouldn't been too bad now would it? The strongest undead would only have 50% more stat than you.
So please do not go "WTF level 1 VS level 15?! That @#%& unfair!" when you don;t even have the slightest idea of how something works.