Don't be greedy. Sorcerous dagger is a shitty weapon, ASMB is astronomically better and is, as of now, BIS for casters. There is no reason why he shouldn't be allowed to bid on his BIS weapon just because you "need it more". That's the difference between a loot council and DKP system. If it wasn't BIS I would consider your argument, but you can't expect someone to be forbidden from bidding on the best caster weapon in the game just because their weapon is SLIGHTLY better than yours. I'm going to ASSUME that you have Mind Carver, which means he only has 8 spellpower more than you with Sorcerous Dagger. If you don't have mind carver than you don't deserve to bid on the mageblade any more than he does considering you couldn't be bothered to work on your pre-raid gear.
TL:DR, yes he should be allowed to bid. Don't be greedy.