I don't think it's a fact that 50% of players in every match are using thorn. Who knows maybe they are I don't really pay attention to the weapon on the guy I just killed :) But seriously, I encountered it from time to time in this last iron banner, but no more than I came across tlw, red death, vex, felwinters, etc. It's a common favorite in crucible for sure, but I don't seem to have any more trouble fighting thorn users vs users of other weapons. You win some you lose some. Lot depends on who gets the drop on who, and taking cover before the other guy gets too many shots into you if its not going your way.