i really dont see the problem. it gives everyone a little bit of common ground. if im not mistaken. we dont become dragonborn. we were born that way. or am i getting something wrong? and why would you not want to be? if you werent then you wouldnt be able to use the dragon shouts.
i would be more concerned about all of us having to be prisoners. (which i also have no problem with)
you are whoever you say you are. People that make a lot of characters who have their own prerogative etc. may have no interest, desire, or even the skill to tackle world changing events. The farmer, or street performer couldn't care less about Skyrim in fighting, or dragons. the great thing about all TES is the ability to say "Sorry Esbern/fate/the gods etc. the prophecy was wrong. In fact, I was never even incarcerated, it was just a nightmare brought on by a bit of undigested potato."
Of the dozens of characters that Ill make, only a small handful will have the ability, or desire to be Dragonborn/save Skyrim/Nirn etc.