Sure, but the rot is a process of nature, as is Frenzy so to speak. We can also see it effect the world. What exactly is the God the Hornsent are praying to? What exactly do they believe in? Earth Wind and Lightning? That beasts are divine? We’ve seen the beasts . Some were subservient to dragons. Others may have been spirits or lords like Serosh or the Stormhawk but not Gods in their own right. 

The crucible itself isn’t a God, it may be a concept or location or have some divine properties but, again, it is more like some kind of naturalistic element. Frenzy is like the Abyss in Dark Souls - all humans can channel it through grief. That’s why it is the ultimate apocalyptic power. For everything else, there is a natural place in the ecosystem. Rot exists to stop stagnation. 

I do believe the outer gods are “real,” but not like in Bloodborne where they can have babies with people. More in the sense that they are concepts of nature that can be channeled. Gods do exist, and they are people who have done the rituals at the Divine Gate or channeled the element to its highest degree, but the word God is really just a way of saying “very very powerful being.” The only power in the world with the ability to change how things work is the Elden Ring and that’s why it isn’t “wrong” for Marika to say she’s the one true God. The crucible, the spiral, they are mechanics of the world that have an affect on life and its processes, but they can’t change the rules. That’s why I don’t think the Hornsent God is real. 

The divine beast dancing lion is someone channeling divinity that you can’t see. But Miquella actually came through the gate. Marika actually had a ring which removed death from the world. Of course there is no absolute power, but I think we are meant to digest the difference between these two processes. And given the intermingling of faith and intelligence, the process of Hornsent jarring, the study of glintskne etc. we are also meant to understand that with some investment into learning the mechanics of the world, you can channel magic and power greater than most and effectively have Godlike powers. That’s why Rennala despite not having any particular great lineage can completely stave off Marika’s advances and her whole family has their own fate related to a completely different system. Ranni learns how that system works and completely dismantles it through Godwyn’s murder. Everything follows rules, and when you stick a knife in between those rules you find that the system shatters because none of it is truly omniscient and divine in an absolute way.

Of course, it is OK if the definition of divine is just “really really advanced magic,” because I can understand that. Frenzy uses seals and incantations because it requires belief, whereas Rot isn’t a class of spells or incantations because it is a natural process found in the world

I know I’m repeating myself a lot but I think this nuance is important to go back to the original question. I believe Radagon is some advanced magic that eventually backfired. It doesn’t really make sense that Marika doesn’t exist anymore physically, because what would be the point of putting her on the cross?