As people have pointed out, there is a big difference between "unique" and "disruptive". There's a middle ground too - "Unique with active drawbacks", where the character's uniqueness isn't itself disruptive, but may have issues with integrating into the campaign or party. Here, it's the player conduct when the problems arise that determine whether the character/player is disruptive or not.
As a completely fictional example: My campaign may have centaurs, but adventuring centaurs are unique. 'Tis fine. I warn the player that this is a biped-centric world, and the adventures are going to be a lot of dungeon-crawling and ruin-exploring, and that centaurs (and similar) are going to have real problems interacting with the world. Still want to play a centaur. OK.
Now at this point, there's basically two paths that happen - one of which is (unfortunately) common and disruptive. If the player then comes complaining to me that they can't fit in the bipeds' structures, nor dungeon-crawl into the depths with the rest of party, and throwing a tantrum? Disruptive - and also not my problem, as warnings were given. On the other branch, if the player comes to me and says, "OK, I see what you meant, my bad. I'd still like to play my centaur, how can we make this work?" I'll work with that, and the character will probably become more unique.
Now, some may call the first "spotlight-hogging". To me, that's a function of how much the player demands the campaign focuses on their character's needs. Which isn't necessarily a component of the behavior here, but often would be.
Fortunately, I haven't encountered that problem in real life. My disruptive players have been few (thankfully), and for other reasons.