Wizards of High Sorcery are from Dragonlance, so it is in fact Greyhawk + Dragonlance.
If that's your argument, prove it. How is it Greyhawk + Dragonlance as opposed to Greyhawk + Wizards of High Sorcery? That's what you haven't done. You just repeat "Greyhawk + Dragonlance" as if Maxperson's declarations made it so. All ipso facto. Would you be having this argument if the Wizards of High Sorcery went by some other name at this Greyhawk game? I doubt it. It's only because you recognize what you see as the Dragonlance brand that makes you declare that this is not a "true Greyhawk" game.
The amount mixing is irrelevant. 10000000 + 1 is still 10000000 + 1. It doesn't remain 10000000 just because you want to win an argument.
So let me get this straight. The Greyhawk content, per you in this example, is the "10000000" and the Dragonlance content is the "1"? So nothing has been removed or otherwise altered/retconned in regards to the original "10000000" apart from the addition of the "1"? So how does this "1," regardless of how noticeable it is for your palate, prevent you from playing Greyhawk at this table?
Ungrateful or not, it's not a Reuben if it's not made like Reuben's are made.
So a "true reuben" would never have Thousand Island dressing? Or pastrami? Or add any additional seasoning? I apologize in advance if my personal judgment crosses the line, but your food expectations are so incredibly detached from reality that it astonishes me that you can even function in life.

It seems to me that out of a practical standard, almost the entirety of all culinary dishes and recipes are not concerned with following a non-existent "True Version" but with the idea of "main ingredients."
Watch Chopped or Top Chef sometime. Contestants often tell the judges that they made something, but used different ingredients or didn't cook it in the same fashion as it is supposed to. Those contestants receive negative marks for telling them that it was something that it is not. Then look at the other contestants that tell the judges that they made something inspired by, say a Reuben, and that this is their take on it. They get props if it is good. They've told the judges that it is something new.
It's clear through extended viewing that even "Top Chefs" don't know what they are talking about or that they have an unrealistic, detached-from-reality way of viewing food that can be contradicted from actual cuisine. "This isn't cornbread, because cornbread should be like this," except for all the varieties of cornbread that aren't made that way. And sometimes they don't apply the criterion that you mention fairly or evenly with others. On some episodes, they'll deduct points and in other episodes, they like it. Furthermore, professional chefs often add ingredients to dishes (without telling people) in order for purposes of adding intrigue, mystery, and layers to the flavor. In my experience, good chefs like having you explore the taste of what they prepared and guessing what you are tasting. Chefs don't just want you to taste; they want you to experience, savor, and appreciate. (And damn, I have now worked myself up into a hunger.)
But we are not dealing with professional chefs, Maxperson. This isn't trash reality TV, and you're no top chef. This is a gaming hobby. Unless you were running Greyhawk with Gygax every Greyhawk setting will inherently be "inspired by Greyhawk." (Hopefully you are not offended at how I now have the amusing image in my head of you accusing Gygax of deceit if he ran a Greyhawk campaign that added anything that deviated from published lore.) That is the inherent nature of running campaign settings. That's what settings are: inspiration materials for cooperative world-building possible through tabletop gaming. They have no life in themselves. They are not actual history. They are gaming toolkits.
There is nothing morally wrong with expecting something to, well, be that thing.
There's nothing morally wrong with disappointed expectations, but you didn't stop there, did you?
Here's some more. An Argument from Fallacy is an Argument from Fallacy. It's not a valid argument to just declare a fallacy and leave it at that. Why? Because fallacious or not, the argument can still be true. The sun is hot because it's the sun is circular, and also true. The sun is hot. What I said is also true.
How? Can you explain without circular reasoning and begging the question? What can one feasibly add to Greyhawk while still playing Greyhawk and not Greyhawk + X____? Warforged? Races from other settings? Adventure modules from other settings? Towns from other settings? People from other settings? Is the integrity of running a Greyhawk campaign so easily broken by an organization from another campaign setting? Do you get equally upset when people tell you that they are running X adventure module only for them to deviate from the written book by substituting or adding something else to the adventure? Has that GM lied to you?
There's nothing arbitrary about expecting something to be that thing. If someone tells me they are give me a car and then hand me a balloon, I'm not in the wrong for expecting a car. Reasonable form expectations based on what they are told.
How are you not getting Greyhawk? What exactly about Greyhawk are you not getting from this hypothetical campaign?
I'm always confused when I see or hear people express a desire to avoid everyone making characters together. I...strongly want for no one at my table to have already fully made a character when they get to the table. I've explicitly asked players not to do that, more than once.
It just seems less good, in every possible way, to have everyone make their characters as a group, in a session 0, and have me their to go back and forth with, and bounce ideas around eachother for backgrounds and all that. I can't even fThom what benefit here could be to everyone arriving at the table with a fully made character, with no discussion between them or with me about heir characters.
Agreed. I can sympathize with people wanting to jump into gaming as quick as possible. Gaming is fun, after all. But Session 0 is also fun for me as a player and a GM. Even if I were doing an online game, I would want that Session 0. I don't want the question "How do our/your characters know each other" to ever be an afterthought. It's also nice as a GM to see
how players are building their characters. It's sometimes even required to say, "Just to let you know, I'm just worried that this (e.g. character option) will probably not see much use in the campaign that I have mind."
FR is still FR in my game where the conflict presented in the Sundering books went different ways, Netheril is still around, Myth Drannor is definatley not ruins again, and there is a University built around a new great library on the southern Dragon Coast, which accepts students and teachers from all the great powers of Faerun, and is home to a knighthood made up of sons and daughters of the nations that fought on both sides in the Sundering War. And there are still earhtmotes, a significant genasi population, etc basically all the handwaivy "totally not a retcon" crap either didn't happen, or happened in a way that didn't burn the 4e stuff off the map with extreme prejudice. Unther is returned, but less of it is, more of Tymanther remains, and Unther and Tymanther aren't in a weird Israel-Palestine conflict, because Tymanther is a good neighbor.
I reworked the recent changes to be more about moving the setting forward, and less about pretending 4e never happened.
Because nothing has been taken from he setting. It's no different from playing in the 4e era vs the 2e era vs the 3e era vs the 5e era.
Agreed again. In terms of my values when running a setting, I think it's far more important to adhere to the spirit of the setting than the letter of the setting. That would still feel like Forgotten Realms. Nor do I think that I could accuse you of dishonesty of whether you ran a Forgotten Realms campaign or not.