There are a ton of dungeons with specific, unique item rewards.
And for the last time, how is it forcing a role on you? You just happen to be able to learn dragon shouts faster than the average mortal, which doesn't mean you have to learn them in the first place. There is not one thing in this game that forces you to do the main quest, so there's nothing forcing you to accept your role as Dragonborn. You aren't prevented from being an assassin. You aren't blocked from being a mage. You aren't stonewalled from being a warrior. There are absolutely no limitations placed on your character by having them be Dragonborn (unless you consider the mere label a limiting factor, in which case there's no argument to be had).
Yes.. there are quite a few dungeons with unique rewards, however in the wall-containing dungeons, the "unique" reward is considered the shout, which is the issue. And no nothing is stopping me from being an assassin, but something is stopping me from being -just- an assasin. Because as I've already explained to you, twice, the game constantly pushes the fact that you can indeed do dragonshouts in your face everytime you come upon a word-wall as a reward in a dungeon. You should not have to selective NOT use an ability your character has in order to be whatever you want, that's just bad design.
Your arguement is similar to having your character starting out as a space ranger, having the abilities to use laser rifles, and even starting out with one. Now for everu third dungeon you enter,the unique reward will be a brand new shining rifle your character is pefectly able to use, AND the game telling you "hey, your character CAN infact use this, and you are a spaceranger".