I’m all for designing companions as interesting characters with good stories first, and potential love interests second
Absolutely.
and can understand why writers wouldn’t want to shoehorn in a character specifically created in order to be a romance option for dwarves (or other shorter races).
I dont, to be honest.

You mentioned "shorter races", that may be good point ...
But still, shouldnt it be easier to model Dwarf-Dwarf romance, than Dwarf-Iron Bull?

And yet, while the first they strictly refuse to give us, second we have.

I mean, if there is some technical problem, moral problem, or it just seems disgusting to them ... you can allways just fade screen to black.

Personaly, i LOVE Dwarves, especialy in Dragon Age, Orzammar is my most favourite place in whole Origins ... and i never forgive them that they give so little Dwarf-themed locations to Inquisition.

And i admit it, im mostly not thrilled from cross-species relationships in Fantasy ... i see nothing wrong if that option is there, but still it feels like every character deserves some love from their own.
When you take Inquisition ...
Even Qunari have that option and that is quite uncommon race, compared to Dwarves, so there it would kinda make sense ...
You have, how many 5 humans if i count right? Cullen, Josephine, Cassandra, Blackwall, and Dorian ...
And two Elves ...
If amount of companions is supposed to be a problem, just make one of them a Dwarf. :-/
Blackwall would be excelent Dwarf.

//Edit:
as BioWare confirmed, it was something of an afterthought and is rather underdeveloped as a result
Really? o_O
Well, i didnt even noticed, bcs i never finished replay ... that game have too many ugly, boring and tedious mechanics, to repeat it properly. :-/
especially given the extra content in Trespasser.
Speaking about ...
I wonder how different would be romancing Iron Bull, who will be still loayal to the Qun ... can you even romance him under those circumstances?