MechaTarrasque
Hero
I am not so sure that your average dirt farmer in most D&D worlds actually has any more proof that the gods exist than the average dirt farmer in Homer's time in ancient Greece had (at least in 5e). Remember not every guy out in the woods is a ranger, not every smuck with a sword is a fighter, not every kid with a ouiji board is a warlock, not every singer is a bard, all halflings aren't sorcerers (despite being "lucky" and "being lucky" is basically the sorcerer's origin), even all "barbarians" aren't barbarians, so not every village priest is a cleric. The cleric is an extra special priest who gets rewarded with power from his/her god. It isn't too hard to make that "years of faith, then the burning bush talks to you and you are casting spells."
To be honest, most of the population might not have actual proof that magic exists--that is something that happens far away. Unless I missed it, most of those worlds lack an Internet, so most people are just hearing stories from people with authority.
To be honest, most of the population might not have actual proof that magic exists--that is something that happens far away. Unless I missed it, most of those worlds lack an Internet, so most people are just hearing stories from people with authority.