Originally Posted by NecroRebel
You're also assuming that the monsters are hitting only on a 13+ before the defender's mark is taken into account, but that will usually only be true on the defender themself, so you're not even really stacking as many penalties as you think.
You make a good point about Elites with double attacks, I'll have to go and look a few up.
As for the above, you seem to be assuming that I'm assuming things that I'm not assuming. For instance, yes, a defenders AC will be high, but the defenders mark doesn't give a penalty if the marked creature attacks the defender, so those two things (while not necessarily equal) tend to balance each other out.
Don't be too eager to rush in with minor nitpicks, there is a lot of highly abstract hand waving going on.