But here's the thing... The absence of something in previous edition doesn't mean that the setting is encased in amber and not allowed to grow with and assimilate new options introduced to the game. Adding in a platoon of dwarven wizards doesn't rewrite the setting, it just introduces a new facet that was afore unbeknownst.
Well, actually... There's Melf and his favorite acid arrows.
You mean during 1e, when
Unearthed Arcana allowed elves to become high priests (assuming they have the necessary ability scores).
They didn't have to at all, they just decided (without my input, no less

) and ruined things in so doing. They could have simply hand-waved the differences away and no one would have blinked.
Because they unwarrantedly believe that they needed to do that in the change from 1e to 2e for some reason I cannot fathom. However, FR was spared a RSE when it was upgraded to 3e.
Well, Dark Sun and Ravenloft both had RESs in the middle of an edition. And FR had the Horde shaking some realms.