All things in the Cosmos have a system. Chaos' "system" is to bring about mindless destruction, and Order is meant to counter that. The Pantheon of Death exists to provide an afterlife for those that die within the physical universe, and the Arbiter exists to transport the souls to their respective afterlives, as well as bring about Anima to those realms. Life is that but of the opposite force. Light and Shadow work similarly in their own ways. The entire Cosmic Chart is a balance.
You can provide this "Death is affected by Order" argument to the entire chart with this logic. Doesn't mean you're right. The Titans are connected to the Pantheon of Death the same way they are connected to the Void Lords, the Demons, the Naaru's keepers, etc.
"I really doubt there was always an Arbiter, a Pantheon and a strictly regimented system of death." She's literally argued to be older than the Titans on accounts, and Oribos is literally a giant city made by the First Ones. Why would the Arbiter be made by the Titans when everything argues against that?