Bedrockgames
I post in the voice of Christopher Walken
It would very much depend on the campaign as well as other player's expectations. I mostly run wuxia campaigns and I use a system built around kung fu techniques (players can acquire these by finding them in manuals, finding masters who know them, and joining sects that posses them; they can also master techniques through training on their own but this is more involved). Because the kung fu technique system is intentionally unbalanced (it has spikes in power to reflect the genre), if a player was cleary just asking to be the son of a given character because he knew that character had the most powerful technique in the game, that might be an issue (though I have to say it might not be depending on the group). Generally if I have misgivings I will suggest the player try something else, but if the player is adamant, I might ask the other players how they feel (sometimes players don't mind another character starting out pretty awesome; and that is within genre). In terms of busting the setting, for me this is usually more about genre. Like I said I am running wuxia so if a player tries to bring in a character background that really doesn't fit, I might suggest something else. And I mean like it doesn't make sense culturally or it feels super strange and out of place. This sort of thing very rarely arises as an issue though
Another example of a power grab is the classic "I am a the son of the emperor". Now that can very much work in a wuxia campaign, and so I am not going to say 'no' right off the bat. But we are going to have a conversation about it.
