The question was why it wouldn't evolve to NOT fit. I think it's a valid question, but it does have an explanation. The answer lies in the population ratio of prey to predator. A deer's adaptive advantages are more efficiently geared differently from the predator's, whose survival of species is more tied to its capture of prey than its reproductive or other functions, unlike the deer.
No, the creationist's point wasn't that sensible. It really was what I said.