So I ask you all: for the game you are currently running at your table, how important is the published lore?
Exactly. The lore is the baseline we can use to meaningfully talk about an established setting. “It’s Dark Sun plus X, minus Y” is way easier than having to completely detail every bit and bob of the world.If I'm playing in an established world, I use the lore as it sets expectations at a baseline, that everyone who shares knowledge/interest in that 'shared world' can understand.
Not to say you cannot deviate from it, but if my Waterdeep is actually a hamlet, and players come in knowing what Waterdeep actually is, how is that helpful to anyone?