A sort of nerf is planned as far as I know, it will be impossible for an arrow to for example, shoot several internal organs that are far apart, and then get lodged into the spine.
This is the most dangerous thing about arrows, just the damage is fine, but if you're going to make your own adjustments to it, you can try making it blunt damage(Like hammers and maces), blunt damage will not be anywhere near as lethal, but won't take away all their power either.
On good hits:
Axes/swords cut off limbs
Spears/arrows/bolts pierce the target(And may injure vital organs)
Maces/hammers will blow away the opponent(Axes too, but less)
Whips cause gore damage, which is to say, lots of pain, and a chance to rip off chunks(Lethal if it hits the neck/throat)
Besides that, you can claim the powerful arrows as realism, as a single arrow would drop an unarmored person wherever it hits, in fact, going by realism, arrows in DF are even underpowered, as a legendary dwarf can take several arrows and still keep fighting.
As for spears, they aren't that useful in fort mode, since the mentioned speardwarf behaviour, getting stuck in a target, and in general not being good against multiple targets(Like the 6+ groups of wrestlers in every kind of attack) With a fairly skilled user, a spear is very lethal, it's a close range arrow, and the twisting can and most of the time will cause targets with little toughness to faint. Besides that, it can easily pierce vital organs, which is a quick way to kill something.
Spears also cause more sparring injuries then normal(Especially fatal ones and spine injuries), so yes, in general, spears are bad to use in fort mode, but they can be extremely good weapons in adventure mode.
Besides that, a champion with legendary in his/her weaponskill can and most likely will destroy goblin sieges on his own, no matter the weapon, the only difference is how long it takes for them to do so.