If you had a MW GGS, you'd know that it only does 35 pierce on the stab, which is around the same as the stab on the poleaxe, awlpikes, double-sided lance, etc.
Actually, come to think of it, the poleaxe is superior in almost every way, except for a couple points of pierce on the stab:
Mighty Poleaxe
weapon length: 141
speed rating: 90
thrust damage: 33 pierce
swing damage: 43 cut
Cost: 14470
Masterwork German Greatsword
weapon length: 123
speed rating: 89
thrust damage: 35 pierce
swing damage: 28 cut
Cost: 15192
NO OVERHEAD
Or, if you really want that extra two pierce damage:
Masterwork Double Sided Lance
weapon length: 130
speed rating: 94
thrust damage: 35 pierce
swing damage: 20 blunt
Cost: 8427
Anyway, the point is that there are polearms that fill the same role, but better, and for cheaper. Why not give 2h some variety?