From my experience its not "getting harder". My dungeon runs have usually been the same since I started the game back when like 3.3 came out. I havent noticed a frequency increase in this, but you'll always have that one group of dps or healers that try to race you to mobs or bosses for some reason, even when youre doing big pulls. They wont even have stacks of whatever they get stacks of built up. I dont get it.