--snip--
I think it'd be a definite improvement to the game as a whole if the idea of 'set sexualities' went beyond the small pool of romances and expanded to include all the companions altogether and important or at least named NPCs. (As in have representation of more than just 'presumed straight' in the pool of characters you interact with...)
I think sometimes when you hear 'we're going to set sexualities' as opposed to 'all bi', it translates to 'fewer cases of representation' even if it's not true or fair. But a lot of that comes from nearly all representation being from the romances. If they actually had more representation outside of romances, perhaps there wouldn't be as much of a resistance to it.
I know that I wasn't opposed to the theory of how the ME3 romances were to play out, but the implementation could have used a bit of work.
Though, on the notion of fairness. I do agree that what's fair to one person isn't necessarily what another considers fair. And if we're all being honest, most of us would consider 'I'm upset that I'm gated from X' = 'this is unfair'.
I do think as long as there's a reasonable attempt to provide options to everyone. You might not always like those options, but just HAVING options is a good thing. Unfair to me is not having options at all.
On the topic of 'main romances', I do think that what tends to be perceived as a main romance, are ones that are tied to the plot and have more romantic scenes.
In ME3, Garrus is one of the first squaddies you pick up, has at least a romantic line in all his little cutscenes, even has a few extra lines in the DLC on top of the "romance" scenes as opposed to say...Steve or Samantha, who basically get the romance scenes, and little else.
In DA:O, Morrigan and Alistair had more content simply because your Warden could see them again after Origins was over. You got some semblance of closure with Morrigan in Witch Hunt, and depending on your choices, could at least see Alistair in Awakening. Plus, both of them were more central to the plot than either Leliana and Zevran were.
In DA:2, I think they did a better job of not having a "main" romance. Isabela, Anders, and Fenris were all fairly equal in terms of importance. (Merrill really was divorced from most of the plot after the quest of retrieving her.) And the main companions seemed to be Varric and Aveline--as they got most of the bonus cut-scenes.
Now, it seems the big thing is in terms of how to make a romance not feel 'inferior' depends on how soon you can recruit them. If you get them near the tail-end of the game, they're going to feel tacked on. If you only get to take them with you (if you can take them with you at all), when the game's mostly done...it's gonna feel inferior to the people who get their romance first thing. (This is one of the best reasons why I hope Cassandra is bi and can be in love with my Inquisitor).
And to make the NPC romances not feel as 'lesser' than the companion ones, hopefully get them really early into the game and have more than just the same, repeating ambient dialogue after you get your one or two romance dialogues.
tl;dr I think so long as people don't have to wait way too long to get their options, the issue of unfairness will be minimized. As well as having the NPC romances as balanced with the companion ones as much as possible.