If indeed DHMG is Dorian. I admit it is likely, but not at all certain. And even if true, what do we really know about him (or Sera, or the IB, or even Solas for that matter)? We know his nationality and class (I mean social class), perhaps also a tiny bit about his politics, but that's all. Not so long ago people were certain Solas was Dorian.
In the case of Solas, what do we know about him beyond his name?
What we know so far:
Cassandra, Cullen, Varric, and Vivienne - enough that I don't feel like summarizing it here, but there's a fair amount out there.
DHMG/Dorian - ”Dorian Pavus is a Tevinter magister. The title conjures fear of arcane master who once enslaved nations. Dorian may wield the power of the magisters, but he delights in not being what you would expect. Brazen and clever, this outcast is on a crusade to rid his homeland of its corruption.”
Iron Bull - ”The Iron Bull is a long way from home, and he prefers it that way. A slap in the face of typically humorless Qunari(Kossith), he loves drinking, killing and looting- but not necessarily in that order. The head of a vicious mercenary company, he’s known for excellent pay and brutal punishment. It’s been a decade-long party, but the Bull may find that old loyalties die hard.”
Sera - "Sera is young, frenetic, and a brat through and through. She revels in the athleticism of being an elf, of being different. But her culture isn’t elven, or for that matter strictly human. It’s the underbelly of the city in her network of rogues; what you do it more important than where you’re from, and friends open more doors than titles. Robs from the rich to keep for herself.”
Solas - we know that he is an expert on the fade, but that's about it, to be honest.
The descriptions of Dorian, Iron Bull, and Sera are certainly enough for us to get an idea if we think we will like them or not. Add that to their looks, it makes sense that people can base whether they might be interested in romancing them based on what we know. I don't think there's anything odd about speculation with the information we have about them. YMMV, though.