We tank all of these bosses , and use Druids to heal. Try utilizing some of the new tools otm has provided , the bosses are not meant for a single group. If all that fails , recruit some more team members if you want to kill bosses.
Rangers are not essential to the current boss fights lol
This too, I think one big change is your DPS warriors cant just slap on a shield and tank anymore. Proper stats, shield wall, defensive formation and well timed stuns are all key to using tanks.
Still, I don't believe this is the most efficient way to fight these bosses though. Its unnecessary damage taken.