Sure, the DM can dismiss it, much like the DM can dismiss anything the players do in game that does not align with what the DM wants to happen, and yet DMs frequently accommodate the players instead of being oppressive tyrants. This is no different.
Though from the way DMs on here frequently talk, accomodations of any kind are to be avoided as much as possible.
Sure, some people like Dragonborn warlocks, but I don’t think it’s as many as half-elf wizards and human fighters.
Your choices are, shall we say, rather revealing of your bias. "Since it hasn't replace
the single most popular option or
the second most popular option, it can't actually be that good."
Dragonborn, as of the last official data shared from D&D Beyond where they actually showed a pie chart breakdown, were only just behind half-elves in popularity. IIRC, Warlocks were in the top 5 classes.
Your blithe dismissal of the idea that a game can improve over time seems to be rooted much more in your preference for tradition than in any frank appraisal of fact. And it ignores things like, as I have mentioned before, moving from descending to ascending AC, unified mechanics, and other mechanical developments that are
quite popular.
That
some things can improve or that
some innovations can become part of D&D's DNA does not mean every single old thing was always bad and needing replacement. That's patently foolish. Instead, it means we need to have an open mind about the
ways things have been done in the past. Do we really need to constrain ourselves to Tolkien's shadow? Dragonborn and tieflings and warlocks suggest we do not, and in fact we can benefit rather a lot from growing beyond that shadow and including more things. That is not,
in any way, evidence that we should thus scorn Tolkien's legacy! Just that treating that legacy as the end-all, be-all of fantasy classes and races is unwise. Do we need to constrain ourselves to (say) five narrowly specific save categories that often get used in inscrutable ways, or to AC where massive negative values are great and your AC somehow gets
more negative when you put on a
+4 Elven Chain Shirt? Evidence suggests not, and that there are more effective ways of reaching the same end.
Mechanics can be designed to better fulfill the goal the designer sought in designing them. Aesthetics can grow to include more than they did before, or to give representation to something that was merely a formless desire before. Neither process has value unless we recognize that there is a space there which
has value in it already. You don't renovate a home that's been condemned, you demolish and rebuild it. Renovation is only useful if the structure itself is worth preserving. And that is what things like warlocks and dragonborn are: renovations to D&D, not demolishing it.