DPR calculations are just thought-experiments. They're those riddles ted-ex gives where they tell you that something very specific and incongruent is happening and you have to figure out the best course of action given these strange rules.
The same is with DPR.
DPR is the riddle "Assuming all characters are in-range and capable of having any weapon or feat they choose with maximum resources, which of these two scenarios would you choose if you wanted to go purely for damage."
That's all DPR solves, a riddle. Take away the range stipulation, add cover, add terrain, take some resources away, and restrict options. Now, the actual damage on the board is going to be so wildly different than DPR that DPR is obviously useless. And that's not even everything to account for.