Alikar hits the nail on the head
Faith would be INCREDIBLY important in D&D worlds. When being a member of a faith = access to healing, a surified knowledge of an after life etc, folk would usually be incredibly devout..but not necessarily in their religion, but their god...as faith and religion are
not the same thing.
For example, the local cleric of Lathander maybe a pious, puritannical SOB, whom his paritioners don't like much, but they'd still love their god, ya know?
Priests would
have to live up to the mark. Also, dieties would blow traitorous priests out of their socks, scourge or
geas abusive/slacker ones etc.
When a god exists, whispering into a priests ear:
"Oi! get yer finger out and HELP the paritioners or I will petrify your ass to go with yer brain!" is something that would enocurage action, lol.

If gods rely on faith of worshippers for "Life", then making sure priests do their job is important. Hence D&D "clerics" would be the NORM, not the exception.
People in RL have amazing devotion and courage, even if they are evil, for example, the Waffen SS commited horrors, but bloody hell, they had guts.
So, your clerics of Bane or similar would be much the same, ballsy as hell and not to be messed with!
Another thing I've noted before, is how dangerous such societies can be. Any time in our world, a society has been hell bent for violence, ugh...Rome, British Empire, Germany, Mongol Empire etc...
So, societies like orcs, hobgoblins, some humans, who are consumed with violence, lust to rule...back by priests who can prove that a god approves such....
very bad mojo indeed!
Orcs and especially hobgoblins would not be "1st levle mooks", unless their society is very squalid. Encourage dby fanatical priests, with rela power, they would be damned dangerous. If all hobgoblins do IS prepare or commit war...wow, you'd need doughty dwarves and human archmages to deal with 'em.