The Legendary Weapons are definitely a focus. I was toying around with changing a couple boss drops later to get more keys. The drops that are just buyable armors/weapons or an elixir.
I've been doing a lot of work on the swords as you have Malicore as well who has that as his only magic option.
I don't know how much I can change the stats, but I reduced the initial levels you get some later party members so you have more time to use Nethercite as they level.