There's a lot about this in the old 2e cleric sourcebook Earth Air Fire and Water.
If I can get hold of it, I will check it out.
According to that (largely excellent) book, there isn't really an elemental religion as such.
A not "really" religion sounds more like a philosophy. Consider reallife philosophical Buddhism. But Daoism works pretty well. Dao can often be philosophical and sometimes maveric, but still engages concrete examples of yang and yin, and even has its own elementalism. Daoism is a religion, of course. But its customs include things like Feng Shui art and architecture, and cooking skills. Daoist alchemy includes medicine, healing, and methods to become immortal (often leaving the mortal body behind). Loose inspiration from Daoist practices seems great for Dark Sun religion.
The elements are not worshipped by a community so much as they're bargained with, or the demands of the clerics are accepted in exchange for magical assistance.
Bargaining sounds more personal, than impersonal.
I view harmony with an element as more like Zen, becoming the element. And doing so by achieving the Dao, oneness with the telekinetic force of the infinite mind. Compare Avatar The Last Airbender.
Elemental clerics are much more inspired by anchorites or holy hermits - weird and possibly crazed people who find ecstatic inspiration in the raw wild places of pure elemental power (mountains, volcanoes, springs, wind-whipped rock spires, etc).
... From a social point of view, Athas generally reverses the conventional roles of druid and cleric. Druids are 'think local' community-builders, clerics are outsider weirdos in the wilderness.
Holy hermits works great. Iconoclasts can feel detached, mystics contemplating the no-thing-ness of the infinite mind can feel out-of-touch. Journeys to the wilderness where a particular element dominates feels awesome. Flatlands or caves for earth. Blasted deserts or volcanos for fire. Atop steep cliffs for Air. Water is so precious − any water anywhere.
But even holy hermits have communities.
They bargain with the elemental spirits - power in exchange for promoting the well-being of the element and its spirits, which is normally defined as opposing defiling and the degradation of the environment.
• The earth spirits want earth to be fertile and un-defiled,
• the water spirits want lakes and rivers,
• the fire spirits want grasslands and forests that can burn and be rejuvenated, etc etc.
And then there's the paraelemental spirits of silt, sun, magma, and rain who (with the obvious exception of rain) represent the actual current-day reality of Athas and grow strong from the desolation.
(Yes, this interpretation obviously contradicts the portrayal of the most prominent follower of the paraelements in the setting, the sun cleric Caelum from the Prism Pentad, but since when has Athasian cosmology ever been consistent?)
I would leave any personifying spirits to the Druids. Except for actual Elementals from the Elemental Planes. But even then, when a Cleric summons an Elemental, I would flavor the Elemental as inhuman. Simply shifting element, never forming a recognizable shape.
The Elementals are made out of an element, similar to the way a human is made out of organic chemistry. In a way, an Elemental is a psionic mind that is telekinetically animating the element. I view the Cleric as attuning to the element itself at a deeper level. Of course, the mind of an Elemental creature is also of interest. The mind of an Elemental is repqpp to the infinite mind that manifests all elements. Perhaps some Elementals are actually transmogrified Clerics who gave up their Human nature to take on an Elemental nature.
Paraelementals seem nonsystematic. 5e has things like Storm and Smoke as paraelementals. If elements divide between Air-Water versus Earth-Fire, then Magma and Rain the primary paraelementals. Because Rain is aspirational, perhaps it gets watery silt and airy sun instead.
Magma: earth-fire
Rain: air-water
− Silt: water-earth
− Sun: air-fire
Magma is valuable because it can forge stone weapons and even shape stone armor. For example, weapons of obsidian, quarts, etcetera are razor sharp and effective. And can deal serious slashing and piercing damage, until breakage.
Anyway, this all does sound very druidic, you're 100% right, and it's a good observation about the inhuman nature of the spirits that elemental clerics deal with vs the very personalised ones that druids work.
