Polymorph is good with anything, as it gives useful utility spells. I would not see it as a damage school. So your damage would mainly come from Necromancer.
I see it a bit of a waste to skip some great Necromancer snyergies. It goes well with Hydrosophist or Warfare or Scoundrel.
It does not synergize but maybe complement other magical schools, for the reason that Necro deals physical damage and most other magical skills deal magical damage. For a mixed group that seems ok, maybe even better for later big-armor-of-one-kind enemies.
My main is a Necro/Hydro/Warfare/Poly combination, using one-handed and shield, and it feels good till now. With a two-handed weapon it should be great, too.
