After really digging in Forgotten Realms Campaign Setting 3.0, my perception of the deity system has changed. Honestly, it's clear that the deity system falls in line with what Forgotten Realms asks of the PCs.
FR Campaign Setting, pg. 93 wrote:Some Faerunians zealously follow one deity. Others make sacrifices to many deities, while upholding one as their personal patron. Still others sacrifice to as many deities as possible, shifting allegiances as their circumstances and needs warrant. It's a rare Faerunian who hasn't occasionally hoped to avert the baleful influence of an evil deity with a propitious gift, or thanked a good power for an unexpected blessing. The belief system of most Faerunians generally centers on a particular deity who's interests and influences are most likely to affect them, but acknowledges other gods as significant and important, too.
This changes my position on how Arelith represents deities. The setting book doesn't go into percentages of these three types of worshipers, but the majority of Faerunians have selected a patron deity that aligns to their interests. In this way, the deity system we have currently aligns with that. A big component that I think Arelith misses mechanically are the ideas of boon or baleful influence.
Because we select a patron deity, the majority of religious roleplay usually focuses on that first group of worshipers: the zealots. There's nothing wrong with zealots, except that throughout the rest of the book there are examples of even religiously aligned clerics giving thanks to Tymora for a lucky shot, or preparing for battle with an offering to Tempus, and more importantly offering sacrifices to evil deities to evade their wrath.
Importantly, it seems that the forgotten realms setting really impresses the idea of ying-yang with deities.
FR Campaign Setting, pg. 93 wrote: Divine magic can play a significant role in society, but not always through the direct intercession of a druid or cleric wielding divine spells. Deities of prosperity and plenty, such as Chauntea, answer their worshipers' prayers with abundant harvests and fair weather. Gods of plague and famine—Talona, primarily—demand placation and send all manner of blights and epidemics against those foolish enough to deny their power. These supernatural influences tend to balance each other, with the extremes of bounty and famine generally unlikely to occur. Chauntea finds a way to bring forth some sustenance in even the worst blights, and Talona manages to mar even the most plentiful harvest in some way.
I take that sort of influence as something that might happen at the macro-level, however I could see individuals bearing a heavier burden if they chose to curse, slander, or ignore a god's influence.
Tying this together, I think that Arelith's system models the setting well, but there's room for improvement. The transient nature of non-divine characters should not be punished with an XP hit and negative piety. In fact, I think that sort of behavior should be encouraged. For divine characters, there is a specific way in which they switch deities (going on a quest to prove their worth) and the XP loss and piety loss make sense in this situation.
Mechanically, this does pose some issues for transient worshipers in the fact that they might shift to Gond to do crafting, and shift back to Mystra for enchanting, but the Campaign Setting seems to encourage that type of behavior in non-divine characters. Of course a smith would turn to worshiping Gond when attempting to complete a task, and turn to Tempus for blessing during his next adventure against an unknown foe.
I think having locations where non-divine characters could provide an offering for a temporary or permanent deity change might be worthwhile to promote the transient nature of faith for non-divine classes.
One last piece I'd like to impress is that religious characters are not opposed to any deity, but they are opposed to their faiths. The deities seem to hold an almost aloof presence, and I think Silvard really gave a great comparison on Arelith Discord 3.0:
Silvard wrote:I think a better comparison is YouTubers and their subscribers. They don't really care about them in that they're by and large an impersonal number, but their income is based on how many subs and views they have so some put up a show for them, others are pretty dismissive or disrespectful but that plays into their audience, but they mostly stick to their niche and people follow them because they like it.
Deities care about their followers, but on an impersonal level. Conflict between religion is ultimately against the faiths and beliefs of those deities, and not the deities themselves. A paladin of Torm might dislike the faith of Bane, but might also note that even a lawful good society can be tyrannical in some nature and be mindful of tyranny's influence.