If two people are forced to face each other, in a building(let's say final storm), 1v1 situation, purely mastiff vs PK, and both have purple evo. If both people see each other at the same exact time and both fire at the same exact time, both hitting their shots to the head (pretend ping isn't a factor here, too) the mastiff will win.

This is the most convoluted, bullshit reasoning I've ever seen. I don't even think it's true, regardless, because the two guns are indistinguishable from a DPS perspective, while the PK has more consistent damage due to a better spread that can be reliably hipfired at a larger range than the mastiff, leaving you more mobility with which to try and out maneuver your opponent's shots. You're literally just creating some super niche, specific situation(that never happens in real gameplay) to try and give the mastiff the tiniest bit of an advantage, and sincerely, I still don't think even then your mastiff wins in that made up scenario.

No game ever plays out like this - in endgame situations like this, you will always have cover in the form of your teammates downed shields which favors the PK. The mastiff is inferior. Refusing to admit this is pure stubbornness and border lining on conspiracy theory levels of denial.