Oh yeah, for sure.  You can break any and every rule you want as long as you know why you're breaking it and do t with confidence.  Even when it's played straight, the "my entire family was killed and I'm the chosen one" cliche can be done well on the hands of a good writer, though it probably comes down to, are you writing a character with this backstory, or are you writing a power fantasy with this backstory.

I probably shouldn't complain too much since this player was very open towards changing the sheet to go with whatever suggestions and critiques me and other GMs suggested with no hassle.

Then again, when I tried explaining to him why describing a character as "Well built for the Asian Arts" makes both zero sense, sound dumb, and is just unhelpful since Asia is, y'know, an enormous contienent with multiple different cultures and countries, he responds with:

"I'll focus down to one or two martial arts.  Despite them being so similar in all.  I have a black belt in Tae Kwon Do, I know the differences."  

????????????????????