The Bec is certainly a bit odd though I'm not sure it needs too much of a change. When I do get hit by a Bec it does frequently seem to strike sooner than it "should" -- maybe it's the animation, which really wouldn't be the weapon's fault or the fault of bad balancing anyway. Add in the silly stun effect and occasionally getting hit a second time before you can block and that's probably where most of the problem is.
It's definitely overused, but the funny thing about gamers as a whole is that they are like water and overwhelmingly take the path of least resistance and thus naturally gravitate to the most powerful and effective weapons/spells/skills/etc. Its been true of every game released over the past 30 years and is no different in this game. So, weapons that are overused are by their very nature clearly providing a tangible benefit to the player. The Bec clearly fits the bill, but how out of balance is it? If at all, probably not much.
And, on the Battle vs Siege tangent. I may not have enough time on Battle to speak with finality, but the ONLY real skill difference I see on Battle is with archers - but again this also seems to correlate highly with map design -- not to mention the simple safety in numbers you get from archers on Siege. Rather the real difference seems to be purely the average level of the character on Siege vs Battle. I see far more peasants and folks grinding on Siege, but I find killing folks on Battle no more difficult than Siege -- there are just a few more freebies with each Siege run.