That's not toxic, chain pulling trash groups is the norm @70, in my experience maybe out of every 50 runs 1 run is a tank that single group kills and he is a newbie to dungeon 9 out of 10 times(or a really bad tank that 1 time). You are not suppose to pull kill one trash group at a time, but drag trash groups until you hit the "trash barrier wall" (ie walls that break when you kill all trash). Of course if your tank/healer/dps suck you pull less.