Yeah that is one of the biggest problems right now, after getting all charms the soulstone farming is still slow.
I was planning more content to fill the gap, but as I am not currently actively working on the next update, I'll try to at least add one more charm to speed it up for now! (This weekend I hope!)
Hopefully I finish my other plans soon and start actively working on this project again? :3 (No promises when or how, yet.)