summon druid with CE can clear anything in regular game naked. With minimal gear, inferno portals in a5. Even faster now that you don't need corpses to raise skellies. Throw in a fana pally for support, and he's gonna be a beast as soon as he's leveled.
That's what they do though they cheese things down with massive tanks. There is no real middle ground unfortunately for a summoner necromancer. They are slow to kill without proper gear though, and definitely won't be doing actual bosses without proper gear.