PoF mobs aren't that difficult if you have the basics of dodging. There is a big difference when it comes to core tyria and then HoT and PoF. In the expansions they expected people to dodge and avoid telegraphed abilities, if you don't you get punished much harder. They also have more health so if you don't know your class well enough the fights will be much longer.
I am fine with their difficulty but I don't think they should raise the difficulty at all for future expansions, its nice not to just steam roll everything.