Returning to the non-compromise of "literally just a human with the name 'Dragonborn' applied somewhere", the reason I don't see that as any form of compromise is that the GM did not actually surrender...anything. Like anything at all. As was previously said by
@soviet, in any game with anything remotely like a player's ability to write their own backstory, the player could
already do that. Hence, nothing was actually "given" by the GM--they offered "you can do literally things you already could do, in return for not getting anything of what you actually want." That's not a compromise, by any definition of the word.
Nothing was given.
The absolute bare-minimum "I have to agree that that is, in fact, a compromise" would be something like this: "Look, you can't play a dragonborn. Would you be okay with playing a human who has dragonborn stats, and we reflavor your breath as you having studied circus performance stuff. You can have a free Origin feat instead of the draconic flight, because I can't think of a way to reflavor that. Deal?"
That's a give and take, even if it is 90% GM take, 10% GM give IMO. You can have some of the mechanics of dragonborn, but none of the aesthetics, and there's a patch to cover the one mechanic that the GM won't permit. I can see some portion of dragonborn fans accepting this. I don't think it would be a very big proportion, but its size is not the relevant question here.
Conversely, "you are the random product of a magical experiment gone awry, totally unique in this world and without any special assocation with dragons" seems to me the 90% GM give, 10% GM take compromise, the logical reverse of the previous. It gives the player nearly everything they want, other than the outright explicit link to dragons and the existence of a culture to which said character might belong, with a basic but serviceable excuse for the character's existence. I would not expect any hardline anti-dragonborn GMs (which are
very much a real thing) to accept this compromise, but I could see a small but reasonable proportion of "my world just doesn't have dragonborn" GMs accepting this. Again, the size is not the relevant concern, but rather whether it actually does involve both sides giving concessions to the other.
"You're canonically a lizardman, perhaps from a distant/insular tribe, and can use dragonborn mechanics" would IMO be the middle-of-the-road option, assuming lizardmen are a thing. Possibly with the "Origin feat instead of flight" swap, and/or "your breath must be acid, fire, or poison type". Getting (most of) the mechanics and some of the aesthetics, but not getting any connection to dragons nor any cultural associations the player might desire. I would expect most GMs that are actually participating in good faith to accept this as a compromise, unless (as noted) there also aren't lizardmen in this world, but...well, there we
are kinda getting into the "okay so what DO you permit?" territory.
Other points on the scale could be (as noted) "you look like a scaly human" (mostly GM, but a bit of player), "you're actually an awakened komodo that somehow became bipedal" (slightly more GM-favoring than player-favoring), or "you are a dragonborn, but you come from another plane of existence where such creatures actually exist" (mostly player, but a bit of GM), or "you are the result of a dragon siring children with a lizardfolk tribe long ago, so you have a touch of the dragon in you but you'll use a blend of dragonborn and lizardfolk mechanics" (pretty neutral, possibly slightly GM-leaning?)