My point is that the concept of the cleric is theistic. I have no problem with someone playing a different class with a different narrative, but the cleric presumes a divine obligation, just like a warlock gets power from a pact with their patron, who shouldn't be giving them power for nothing.
Nontheistic clerics make no sense to me.
Yes, but no matter how many times you say that, "you're playing the game wrong" isn't a good or convincing argument. Especially since there has been a basis in this for decades in D&D. If a player wants to play a character that gains power from extreme belief in something that isn't a deity or devotion to a philosophy, what class would you recommend them to play? Would you tell them that they have a bad idea and they should feel bad for liking it, or would you slightly adjust your assumptions about the narrative of a fictional class to accommodate your player's character concept? Or would you go through the trouble of homebrewing a whole new class (probably poorly balanced, because this would be the first playtest) that you'll only use once or twice?
And, again, there is precedent in traditional D&D. That's what your precious "lore fidelity" means, right? There've been deity-less clerics in D&D for longer than I've been alive (the Athar and Athas's elemental clerics). Not to mention settings where they might be the core way to include clerics (Eberron, Ravnica).
In Eberron, it's possible that all Clerics are nontheistic. The gods have never been proven to exist, but divine beings and powers still do. Different people and religions have theories about where clerical magic comes from (the Vassals say that everyone is channeling magic from the Sovereign Host or Dark Six, the Blood of Vol says that everyone draws from their inherently divine blood, some say it comes from collective devotion, etc), but none are stated to be the official source of divine magic.
You're one of the people that makes a big fuss when WotC changes things from older settings. Wouldn't it be revisionist to deny the possibility of godless clerics in the rulebooks?