Would be probably some kind of Evasive tank with bigger area of control since the Range of the spear is higher.
It allows you to hit someone in a hazardous terrain without endangering yourself.
Maybe in a party with 2 casters 1 support (Maybe Summoner/Healer type) ?
But honestly I prefer just a regular 2handed. It only seems the range is the difference (and lower damages?)
I almost want to try it but we have a very limited knowledge of the polymorth skill tree and it really seems more like a spec enhancement rather than an entire spec to focus on.
Keep in mind that if you spend a lot of point in polymorth, you have free stat points so you can spare a few in strength.