Hah, you would have hated the old Draginslayer. It was basically a dev weapon that could insta-kill anything within monster level 100, and in the very early versions of the game you could get it as soon as you upgraded your flight skill to level 5 or so.
Your proposals aren't bad - the Draginslayer is pretty massive, and it should feel hefty in more ways than one - but as with any "meta" weapon developers have to tread carefully; generally speaking, players prefer that other things be buffed as opposed to having a popular meta/weapon getting nerfed (unless it's hilariously overpowered, like it used to be prior to V0.1.6). The more conservative/cautious option would be the addition/buffing of other weapons to help with balance by giving other viable alternatives around the point where you fight/after you fight Slitherss. That's obviously more work, though, and there's a lot of other stuff to develop, so I guess we'll just have to wait and see what Fish has to say about it.