Did this yesterday on my team. Totally agree that the second and last boss are tough. This was my second team to do them on, but I surprisingly one shotted them. Far different than my first attempt, which involved lots of wipes.

I changed up talents and used the 80% speed boost on my pally to stomp about half the flower adds. Popped absolutely everything when they can out - hero, guardian, pain suppression, etc and spammed AOE heals and AOE damage macros. Have to sidestep the cone of boss damage as well, of course. It was close, but survived the flower phase. Second phase flowers I didn't move, maximizing DPS and the boss died just as the horde was coming for me.

Of course, my guys had pretty decent gear - above ilvl 620.