Lightning as a weakness stems from a general lack of understanding of lightning. It should behave as any other rock would against lightning because its just a glowing sentient rock. Gold vs rotten things is just an issue of ghoul/necro lore tho.
When I was working on this and talking to the original writer I was told that gold weakness was actually just something he forgot to edit out and included on accident so I just wrote something to respect how long the lore was sitting like that. Tbh tho blunt gold only is probably a better middle ground and I made an edit based on what you suggested.