I see what you mean, I think it definitely has a big impact how you play the hero. Personally I think placing it in spirit makes the most sense.
Make it 3k souls, 10% weapon damage, 50 bonus health, and no need to add spirit power cause at t3 it gets 12. It's underwhelming stat wise, but that's not the point right? It's good because of how it changes your spells, and possibly playstyle.