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 polestun on the thrust only. Turns pikemen into an effective support role again, rather than the whirliebirds of solo destruction they had devolved into.