Started this off as a comment, but developed into something large enough to be a post. The following is my interpretation and not the only way of understanding the lore:
There are many different beings of great power in the world of Runeterra. However, even among themselves, these “gods” vary massively in their individual strength. Some are world forming creation gods while others are perhaps only a few hundred times stronger than a normal human. To help create some sort of understanding, the following tiers are helpful:
Tiers of gods
* Greater gods: Present at/before creation
* Medium gods: Interplanetary forces
* Lesser gods: planet bound dieties
* Demi-gods: Gifted divinity
Right now, there are very few Greater gods we are aware of, including beings such as Aurelion Sol, Bard, and the Watchers. They wield powers on the level of the cosmos and are by far the most powerful beings we know of. Able to forge stars or warp reality, there is a massive difference between them and any of the other gods. They were present from the begining, aware of it or not, and are fundamental forces of the universe.
The best examples we have are the Aspects of Targon, not to be confused with their Chosen (we’ll get to them later). Aspects seem to exist separate of their various hosts, so that a chosen could die but the Aspect lives on. Their powers reach to multiple worlds, but are clearly not creation level power. The Targonians had to use trickery to control Aurelion Sol, and even then it was only the destruction of his stars that kept him in line. Two other notable traits many medium gods share are that they usually embody some universal force found everywhere life is (Death, Justice, Sun) and are usually immaterial most of the time.
Able to alter landscapes and weave divine influence over mortals, Lesser gods are still nearly incomprehensible compared to a normal human. The likes of Ornn or Volibear, these beings presence alone can alter the area around them. Though they are planet bound, they are far stronger than anything else from their world.
These are the most diverse of all the ranks of gods. These beings are massively more powerful than a normal mortal (see Taric’s color story) but are beneath a Lesser God in that they could not accidentally change terrain around them in a fight. A general rule of thumb is that if the god was created (Ascended, Chosen, Avatar of Volibear) they fall into this category. Some blur the line between Demi- or Lesser god, such as Azir and Xerath, beings substantially more powerful than the other Ascended, while others are tricky to tell if they join this tier, such as some of the Land Spirits of Ionia or deamons like Nocturne.
A massive question mark in the world of the gods. With no known comparison or great demonstration of power that seemed to push it, Nagakaburos could be a Greater god for all we know. Some rioters have hinted at the idea this elder god could be slightly stronger than Aurelion Sol, a truely incredible feat. However, this is far from concrete as it is not from the Universe page. The fact it embodies the concept of moving forward is akin to Aspcets and Medium gods, but is clearly different from them, not part of the Targonian empire or creating Chosen vessels to do its will. Hopefully we learn more about this cryptic being in the future.
And there you have it. A rundown of the various gods and their rough estimations of power. While each teir of god can have vastly different amounts of power, there are usually pretty distinct “break-points” between one class and the next. Things get a little blurry the farther down you go, but I hope this helps as a starting place when understnading Runeterra and its various Dieties. Until more lore comes out, thank you for reading!