DPR calculatiosn are used to determine how you should build your character, ...
So you are wargaming, not roleplaying, got it. Just remember that some people actually like to roleplay and base their choices on what makes sense for their character, not what is considered 'optimal' by the wargaming crowd.
DPR calculations can be useful to inform your choice between options that make sense for your character. In that case, taking the more effective option makes sense for optimising *for character*.
Oh and before you pull out the Stormwind dead-beat argument again: Stuff. It.
Having math so tight that the difference between 'optimal' and the rest is so small that it doesn't end up 'gimping' your character is a godsend for everyone for whom the rules are a necessary evil to have a game. If you prefer wargaming, that is your problem. You do not get to tell other people how to build their character as much as they get to tell you how to build yours.
So no, DPR calculations determine eff all. They are merely a tool that help weight a decision, nothing more. And you can argue 'but statistics' till the cows come home, I do not care one wit about an extra point of average damage. All I have to make sure is that my toon is good enough, no more, no less. Whatever else character resources are left over after meeting that goal are mine and mine alone to use as I see fit.