UG doesn't really > Dims. UG+physical damage does, but only if the Dim deck is slow on damage.
Dims+healing beats both that AND PC if it's splashed into the UG deck.
However, draw power can let an UG deck OTK before it dies.
Again, the main problem here is the inability to deal with Nymphs (not enough CC, too big deck) and Dragons (too high HP, hard to draw Dims with big deck).