Bhelen does offer to restore your standing in House Aeducan if you side with him. Doesn't he also imply that he's going to pull some strings to lift your exile and remove the charges of fratricide against you? I always figured that he had Trian's death listed officially as a "great unsolved mystery" afterwards, something the Assembly either didn't bother investigating, or seemed to always find something more important to discuss whenever it came up.
Siding with the one who betrayed you, took everything from you, and basically destroyed your entire family (by murdering your older brother, pinning the crime on you so you got exiled to die in the Deep Roads, then either caused your father to die of grief or poisoned him himself) just for the "honor" of being restored to the House (which he got you kicked out of in the first place) but not being restored to your place in line for the throne (ahead of him) is not the same as exposing and killing the bastard, getting back your birthright, and being able to crown yourself.
That'd be like if Howe survived to the end of the Landsmeet and offered to restore your family's lands and titles to your family's name, but you don't actually get to rule Highever as the next Teyrn Cousland, and only if you support him as the new right hand to the new monarch and you don't marry them. You don't get revenge, you don't get your birthright back, you don't get the crown, and you actually have to exalt the man who destroyed your family and took everything from you in order to get that little scrap of goodwill back from him.
Can you imagine what a sh!t-hemmorage Cousland fans would throw if the game did that? Set it up so Howe was the bastard who destroyed your family and stole your birthright, and all game it seemed like eventually you could get revenge and go home, but then the game made it so you can't kill him and/or you can't gain back what he stole from you--or you could but the the only way to gain back your family's stolen lands/titles was to exalt the man who killed them and stole it in the first place?
No! That would never fly for a Human Noble playthrough, yet everyone expects that the Dwarf Noble should be just fine with supporting their traitorous younger brother and just "accept" that they'll never get back what was stolen from them?
Like I said: Orzammar has two subpar choices: Harrowmont or Bhelen. One is more popular than the other but doesn't have a strong claim since he's not from House Aeducan, while the other has a strong claim as the only surviving heir of House Aeducan but is less popular... because he's the only surviving heir. (Having his whole family killed to get there didn't endear him to the Assembly.) I already found it irritating that the game doesn't offer a non-DN a reasonable third option, but it became especially glaring when I played through Orzammar as a Dwarf Noble, and realized you're a reasonable third option. You have a stronger claim than both of them as Endrin's eldest surviving child, and the favorite for the throne before your disgrace.
There's no reason the writers couldn't have included an extra quest chain that gave you the option to clear your name (at least if you were framed for the murder), garner support from various dwarf nobles (much like how the Warden can go around garnering support from human nobles before the Landsmeet), and be able to use the Paragon's crown to crown yourself. (At least, if you did the quest chain beforehand and possibly did a successful persuasion check. If you didn't complete the quest to clear your name and didn't get support from various nobles before reaching Branka, then if you try to crown yourself the Assembly says, "Ah, no. Sit down." But if you did complete the necessary steps beforehand, and/or complete a persuasion check, the Assembly should be able to go with it.)
I mean, structurally DAO takes place in two kingdoms: Ferelden and Orzammar. The Human Noble is from the second most powerful family in Ferelden, and the Dwarf Noble is second in line for the throne (under your older brother) of Orzammar. The Human Noble can become king/queen of Ferelden at the end, so I see no reason why the Dwarf Noble can't become king/queen of Orzammar at the end. Human Noble can become King/Queen of Ferelden, Dwarf Noble can become King/Queen of Orzammar. Boom. Boom.