Because you do not hold the same belief that I do: that the Warden/ Paragon could aid Orzammar post-Blight to aid in proper, long term Reforms? Then I guess I shall continue to be implausible in the eyes of all Bhelen supporters. I can live with that.
The problem is that you really haven't explained your plan in a way that makes it seem at all plausible. From what I remember (and some of it might be wrong), you plan on founding your own house and letting in members of all castes including the casteless that are willing to fight for you. I'm not sure if there is anything anyone in Orzammar can do to try to stop you from letting in every single non-noble if you wanted to but I think realistically there are only so many people you can let in. Letting the casteless join your house appears to be the only way you'll help the casteless in that the few who catch your eye are no longer casteless. This seems to change the fate of the casteless as a whole about as much as noble-hunters becoming technically noble upon the birth of a son does.
You want to use the members of lower castes that join your house and just support you to change the system. Your house has one vote. If you are the dual head of both House DN and House Aeducan (could happen) then that would give you two votes. If you could keep Helmi alive and get him to vote according to his principle's and not those of his mother that's three houses. Three out of eighty-one* will not really get you anywhere. Are you counting on support from other houses? If so, where is the indication that any of them will support you when Helmi's views are so abnormal? Will you count on Bhelen's supporters who all hate you and who have their predecessor dead at your hands during the rebellion? Will you count on Harrowmont supporters who voted with him because they want the throne themselves or because they love the status quo? Do you acknowledge that the nobles in the Assembly are the ones with the political power and that they love the status quo since it's so blatantly in their favor?
Are you going to just hope that the fact that you're a Paragon and that the desperate Assembly, who will even let you pick the ruler yourself if you admit that the Paragon didn't care because they are sick of the stalemate, will let the Paragon cast the tie-breaking vote (and given that they'd be a deshyr, that's the equivalent of giving Harrowmont or Bhelen 41-40) means that Paragons are omnipotent? That nothing you could ever do or say will turn people against you and they will automatically fall in line or commit 'political suicide' even if what you want to do is not even remotely in their best interests?
What about the fact that when Branka wouldn't give Bhelen exclusive golem rights we never hear of any riots when he goes after her? Do you think that if Branka decided to start grabbing people off the streets and forcing them to become golems then the fact that she's a Paragon would mean that everyone would continue to support her and that the deshyrs who tried to stop her would be committing political suicide or is there only so far that the Paragon can push before people stop worshipping them?
Even if your DN became king (and that wouldn't be easy given how much everyone wants to keep the Aeducans off the throne) then Harrowmont proved that the Assembly is still perfectly willing and able to stymie you. Unless you're willing to crack down or dissolve them like the 'dictator' Bhelen does then I honestly don't see how you're going to pull this off.
A complete overhaul of the dwarven system like that on the strength of your being a Paragon when you reject Bhelen's methods highly effective because they are 'immoral' just strikes me as incredibly unrealistic.
*That's another thing I've been wondering about. Are there 80 noble houses in Orzammar currently? Do only the top 80 families get to vote? If you become a Paragon do you get to be a deshyr? If so are there now 81 deshyrs or does the least important house lose their vote?