cmp, you should set the turn rate limit based on the weapon's moment of inertia, (mL^2)/3 for slender rods being held at one end, where m is the mass and L is the length. Obviously this is a simplification, but close enough.
This would satisfy both realism and balance (I don't think anyone ever complained about Long Dagger lolspins).
To compensate, spears/pikes should get 100% chance for the old polestagger on the thrust only. Turns pikemen into an effective support role again, rather than the whirliebirds of solo destruction they had devolved into.
this.
Well if they implemented it in my ideal fashion, you could still turn 180 degrees (or at least 90-135 degrees) after thrusting your weapon, but more than that and you'd lose the thrust animation. You don't see it very often, but sometimes people would jump, thrust, and spin 3 or 4 times before hitting the ground. I think it was to stop that from happening.
if it's possible, the character could just be slowed down that much, that it just wouldn't make any sense to turn around more than 180 degree, because you can't jump and turn as fast as the time of the jump (or run) takes. if it's done right you shouldn't be able to swing/turn around your long-spear in thrusting mode to hit somebody behind you, at any high enough speed at all.
but devs, while you're at, make sure the vertical speed gets into consideration too, if possible.