I believe,haldbards were slightly smaller in lenght than tippical pikes,so,besides keeping enemyes at a distance,it could do a slash in the case the enemy got beyond the tip of the haldberd(pike cannot do it,unless in disciplined,organised formation)...
Oh,and haldbard type troops are usually good armoured so u can't say there so vulnerable 2 arrows...........
Seems that they are the more offensive counterpart of pikes(I'm not talking vs cavalry).
So,apart from holding the enemy,they can DEFEAT it.....