If Ultimator truly emcompassed everything, why would she need to forcibly attempt to overtake the fifth dimension? If this dimension was already a part of herself, why would she need to encorporate it into her being? Granted, Ultimator's powers were far greater than those of the entire race of 5-d imps, but imo she just seemed like more of a dimension-devourer than anything. The PM, however, does encompass the totality of existence - (the original/infinite DC multiverse registering as little more than a germ to it, etc.)