I think Cleric spell selection should be much more focused based on deity. But that's more of a 5e thing than BG3 thing.
Wouldn't it be more domain based than diety and domains being deity based?
The general spell selection all Clerics get is too big.
Clerics of Shar get spells like Guiding Bolt (radiance) and Daylight which thematically oppose their faith. Likewise, Clerics of Lathander get Inflict Wounds (necrotic) that directly oppose birth and life. All Clerics get Flame Strike, Hold Person, healing spells and random utility like Find Traps, regardless of faith.
They're not Wizards. All of their spell selection should fit their deity instead of getting a huge repertoire of all kinds of spells. While there could and should be spells that are universal for all faiths (Bless, Shield of Faith sort of thing), they should never be able use powers that are in direct conflict with their deity's portfolio.
