It's a question of what defines a setting. If I run straight box Forgotten Realms, is it Eberron? I don't think it's a stretch to say I'd get agreement that it's not. The question is what defines a setting, and when do changes made to it start making it a variant, an alternate history, or even not the same setting.
And it's ALL GOOD to do any of those. Want to run an alt-history Forgotten Realms for your table? Go for it, there's no judgement.
But say you wanted to run an alt-history Dark Sun where Rajaat never learned arcane magic, and the Green Age never ended. It would be a richly verdant world with no sorcerer kings, no slaves. Again, could be really cool to run. But if you were putting up a poster in your local FLGS would you just call it a Dark Sun campaign? Or is it far enough away with next to no common points (not even the maps) that you'd feel the need to point out the ways it is not Dark Sun, just inspired by it.
That's all this is - no judgement about what you want to run. It's literally all good.
Just exploring what is a setting, which I believe to be the lore of it - the history, cultures, politics, etc.