Bosses hit harder, but have less hp.
The problem are mobs. They will stunlock your thrall and you’ll lose it. Dalinsia can take care of world bosses, don’t worry. Make sure she has food in her inventory.
Two places where you need to be extra careful: when fighting Thag in the wine cellar dungeon, where you need to clear the wights or they will kill her., and the forge in the Well of Skelos. I haven’t been there since the update, but you need to pull them by groups or they will also kill her. Other than that, just don’t go running inside enemy camps as mobs can kill her too. Go slowly.
During purges, try to have as many thralls as possible fighting in higher numbers. Build a choke point at the entry of your base and open after it, placing your thralls there. That should do it.