Polearm attacks have a much shorter reach than 2h attacks given the same weapon due to their animations.
Polearms tend to be balanced/swing faster/do less damage vs an equivalent effective reach 2h.
These are attempted stats of a 2h equivalent for bec-de-corbin without the unbalanced flag:
Considering that a +3 Bec-de-Corbin (blunt mode) has the following stats:
Masterwork Bec de Corbin
weapon length: 120
weight: 2.8
difficulty: 15
speed rating: 95
thrust damage: 28 pierce
swing damage: 33 blunt
slots: 2
Knockdown
Upkeep: 756 gold
A +3 2h equivalent without the unbalanced flag would be something like:
Mighty Goedenhammer
1h/2h
weapon length: ~104-108
weight: 3.3
difficulty: 14
speed rating: 94
thrust damage: 23p (2h stab?)
swing damage: 33b (around the same as 45c weapons like miaodao)
slots: 2
Can't use on horseback
Knockdown
Upkeep: ~700+ gold
Notes: Seems okay-ish vs Long Iron Mace/Bar Mace as a balanced, longer, weaker, less knockdown/stuns variant as long as it doesn't get horseback capabilities. Definitely OP vs Studded Warclub, though the upkeep is much higher.
Alternatively:
Mighty Bec-de-Morningstar
1h/2h
weapon length: ~80-84
weight: 3.5
difficulty: 15
speed rating: 94
swing damage: 37b (around the same as 49c)
slots: 2
Knockdown
Upkeep: ~700+ gold
Notes: Seems somewhat reasonable vs Morningstar, though Morningstar is generally considered an OP weapon.