Cauvel22

Originally I thought allomancy was the art of preservation, hemalurgy was ruin's, and feruchemy was just kind of there. Later I read something that said allomancy was ruins magic due to it destroying the metal used which made sense to me because hemalurgy was a cosmere-wide thing. Now I've come around to thinking that feruchemy is purely preservation, hemalurgy is wholly from ruin, and then allomancy is the combination of the two. It preserves the user and destroys the metal kind of a thing. This would then also make sense as to why both God metals, atium and lerasium, both have to do with allomancy instead of their respective gods magic. My question now is why hemalurgy is a cosmere-wide magic when ruin is now harmony. Please also let me know if my understanding of the metallic arts is flawed in any way.