I think the time has come to talk about gods, as well as godlike entities that technically aren't gods. There are effectively three types of entity that can be reasonably called 'gods':
Natural Gods, God-Constructs, and Godlike Entities. both natural gods and god-constructs are by definition rooted in the Immaterium, while godlike entities are generally those which do not use it, such as the C'tan or the Tyranid Hivemind.
Gods, Natural and Otherwise
Natural gods, the most prominent of which are the original three Ruinous Powers, are a sort of 'living narrative' created by the impact of psychically active races (even if their impact/sensitivity level is extremely minor) on the Immaterium. Like all living things, they possess a desire to continue living, and do this by spreading their story through worshipers, and exerting their power to bring the materium more in line with their story's themes (generally on a temporary or otherwise limited basis.) This, obviously, can be both good and bad, depending on the god in question, but gods are
rarely fully good or evil. This is because of one key fact:
naturally occurring gods never lose any of their themes or domains, unless specifically stolen by a different god; they simply have different aspects emphasized or deemphasised and new ones added as their story mutates and changes through different forms and people's worship. This makes actually combating a naturally occurring god
extremely difficult, as the primary method of doing so is to turn their own narrative against them with a contradictory one—to face a god of Murder, one might come cast in the role of the Justice-Seeking Hero or the Dread Avenger, and similar themes—yet because naturally-occuring gods can encompass mutually contradictory themes, such as Isha being both the goddess of Nature Unbound
and the goddess of Mastery Over Nature, they can consciously choose to express a different narrative that itself counters yours—and so a battle between gods is as much a matter of each participant pivoting their aspects for advantage, which gives a distinct edge to older gods whose stories have been told and retold and conflated and merged so many times that they encompass vast numbers of different themes. This
also means that the older a god is, the more difficult it is to cut it off from worship—for gods can have many faces and many names, acquired as they age, and so seemingly unrelated cults may be in truth worshiping different faces of the same god.
God-constructs, meanwhile, are deliberate creations of
Godsmithing, a psychic discipline effectively lost to the galaxy with the disappearance of the Old Ones either during or after the War in Heaven (there were enough temporal shenanigans going on in that war that it's not actually clear
when the Old Ones disappeared, chronologically speaking, only that they weren't around by the time the early Aeldari Empire was picking up the pieces in the aftermath), though a handful of races or individuals have worked out the rudiments of the practice since. Because they must be formed whole, god-constructs are effectively incapable of expressing contradictory narratives—even extremely closely related concepts like Brutal Cunning and Cunning Brutality cannot exist in the same god-construct, which is why the Orks have Gork and Mork and not Gorkamorka as originally intended (as the construct fissioned into the Twin Gods in the process of its creation). Similarly, they cannot
gain additional narrative facets unless those facets are in harmony with or supportive of their core narrative, which limits how they can grow to an enormous degree. On the other hand, within their narrative god-constructs are
extremely strong—enough that their narrative can frequently overpower what
should be appropriate counter-narratives.
So what's with the Aeldari gods then?
Simple:
They're both. yes even Slaanesh. This is why the Pantheon is and was so powerful, so unprecedented—they began as natural gods, who can grow and change in ways god-constructs can't, and were then enhanced with Godsmithing by the Old Ones at the pinnacle of that race's power and knowledge of the craft, a height no other (at least in the milky way) has reached before or since. Slaanesh, meanwhile, might be a crude imitation of that peerless skill, but they too are a naturally occurring god who was enhanced by Godsmithing—however crude and fumbling—and
that is how the Dark Prince can match the other three Ruinous Powers despite being but a mayfly in comparison. No god has commanded the Immaterium as Asuryan once did with the Edict, no god could walk unfettered between materium and immaterium as Isha did in her role as Everqueen, no god could hold the fate of
all mortals in hand as Morai-Heg once did—not even the Chaos Gods, however much they might proclaim otherwise. The Pantheon was
unprecedented, and even the original three Ruinous Powers are 'just' especially ancient and powerful natural gods with a truly dizzying breadth of faces, names and themes.
Daemons and Devas
The other major factor is
Daemons and Devas. These are effectively 'subordinate' gods or god-constructs of another, more powerful god—sometimes created by expressing some facet of themselves as an independent entity, sometimes as lesser gods subsumed by a greater god's narrative, and so on. Daemons are specifically those of the Ruinous Powers, and generally fairly malevolent—essentially, all Daemons are Deva, but not all Deva are Daemons. Of course, as they are technically gods themselves, a Deva or Daemon with enough strength can create their
own subordinate Deva or Daemons, who can in turn create their own servants, and so on and so on, each layer empowering every layer above it and being in turn empowered in a highly efficient feedback loop—and here the mad genius of the Old Ones is laid bare, because the Pantheon seemingly had no Deva—because
every Aeldari was technically a Deva of the entire Pantheon, incarnated in flesh. Now, Deva can survive the deaths of the gods they are Deva
of—and even usurp them, becoming the master in that relationship or just outright killing them and taking their place, under the right circumstances—but this requires being what is known as an 'exalted' at minimum. Exalted Deva (or Daemons) are the most powerful of a god's servants, commanding vast legions of subordinate Deva who often command vast legions themselves, and there are rarely more than a handful of such entities at any given time. If only because such beings can grow ambition and seek to cast down a god they serve, as Skarbrand once did. An Exalted with enough strength can
also break free of their servitude, under the right circumstances, taking all their legions of subordinates (and the power they represent) with them, and here went Be'lakor, the First Ascendant of Chaos and now the Lord of Treason.
Godlike Entities
In addition, there are many other entities who can be reasonably called 'gods' despite not even using the Immaterium, such as the Tyranid Hivemind or the C'tan, whose powers are typically rooted in command of the mathematical rules of the Materium rather than the narrative ones of the immaterium. This does not necessarily always hold true, but generally speaking godlike entities are rooted in the Materium, rather than the Immaterium, and their powers—while often resembling those available to gods or their servants—are ultimately rooted in the Real, representing deep understanding of or instinctual command over the natural, causal forces of reality. Though of course, there is nothing which
prohibits such entities from affecting the Immaterium, especially those whose powers are derived from knowledge rather than instinct. Or even on accident, as is the case for the Shadow in the Warp caused by the Hive-mind.
The Anatolian, Adem Kadmon
The Emperor is, like the Aeldari gods, a unique existence: a product of crude godsmithing who is
not a god, a creation that can grow unfettered, a man as flawed and limited as any other yet commanding strength no man can match, a born ruler who has for hundreds of lifetimes rejected a crown, all these things and more. He lives as any other man, growing into his strength and knowledge anew with each life, yet he is undying in a way even the Ruinous Ones cannot undo, reborn again and again throughout human history—though there can be many, many centuries or even millennia between his incarnations as his soul regains its strength from the strain of averting True Death. Most critical he is The Anathema: an impossibility, a paradox: a Pariah whose negative-soul is so impossibly strong it has looped back to present as a normal Psyker of godlike strength, but whose very touch is utterly in opposition to the Gods of the Immaterium. His existence is still yet unknown to any of the major players of the current era, for he has remained in the shadows for the majority of his existence, yet the time is nigh for him to claim his long-rejected crown, however reluctantly, and echos of his opening moves are already being felt—even if it will be centuries yet before his next incarnation is born…