Let's imagine a world where there was a titanomachy, a war of titans vs gods, and the titans lost. Then the titans are cursed to be reincarnated as ordinary mortals, forgetting their past lives.
Later there is a rebellion of the mankind against the gods, and mortals win with the help of the lord feys. Now the feys have replaced the old religion, but with their own problems. The giants are the children of the reincarnations of the titans, and they don't remember the past, but they don't like gods nor lord feys. A new titanomachy starts.
Genies were powerful idols but used as slave soldiers in the first titanomachy. Now many of them are free, and they have become new idols... and tyrants. Other genies are slaves still and they don't like to obey their owners... or they like to cause troubles to mortals, creating new stories of adventures and lucky/unlucky heroes.
Deities have disappeared but their clerics can cast spells, or be summoned as vestige spirits for pact magic. And clerics have got a love-hate relation with the favored souls and the psionic ardents, allies against giants, lord feys and genies, but with a different point of view about theology, or clerical authority. (I imagine favored souls like spontaneous divine spellcasters with armour, but also with special class features like a softer version of monster templates).
In the cities their is a urban version of the druid, the Augur. And the necromancers have got a "rival school", the haruspex, the masters of the flesh-shapers (like the equivalent of biopunk technology of the life-shapers rhul-thaun from Dark Sun or the Yuuzhan Vong from Star Wars legends.