Well for pugs from the realm especially large number of players can be bad
I was yesterday in gates 22 ppl group we pass first 3 bosses with no problems (several dead on shamans only) but then we reach Legendary General Nazgrim
I can told ya that we spend over 2 hours on wipes there (yes in flex) after that time we change many players many left new comes and so one but we manage to down it at last with 11 ppl group with 3 healers the big problem was that boss was nearly 10% before defensive and ppl just stop dps till meanwhile we got swarmed by adds after we decide to ignore defensive and baner and just keep shamans away from him when he is below 15% he dies
So mine opinion is less players in random PuG group makes boss more easy if you get more players then make sure that you will use voicechat