Path of Exile: I decided to play my Raging Spirit Necromancer in The Atlas of Worlds, and wow, is she effective. At level 73 (with 9 Passive Points hanging around unspent) she's way better at clearing maps than my lvl-80 Cyclone Gladiator or my lvl-74 Dominating Blow Guardian. She's terrible in the Mine, and not so good at chasing Abyss cracks. Basically, any time you have to press ahead with some urgency, she's not so great. But otherwise, she's a beast. She's not even that flimsy. You might expect her to be a "glass cannon", and strictly in terms of her own defenses and Life she is, but 23 minions is like having an entire NFL team protecting the QB, the offensive team and the defensive team; when she gets hit, she goes down, but it just doesn't happen that often. Summon Raging Spirit is maybe too effective. Zombies are definitely too effective. And she has no special gear, just run-of-the-mill yellow magic items. It's not outside the realm of possibility that I've simply stumbled upon a perfectly-tuned arrangement of Gems and Passives for her, and all of my other characters are shabbily-assembled.
Sentinels vs. Undead: As minions go, Undead win, hands down. You just summon them. With Dominating Blow and Herald of Purity, your character needs to land effective melee strikes on the enemy to summon the Sentinels, and the Sentinels are on a timer, so you have to start fresh with almost every fight. My Necromancer couldn't fight her own way out of a wet paper bag, but she doesn't have to.