... it would be quite easy to write a potentially unhealthy power imbalance into their relationship. Lavellan would be the object of his affection in quite a literal sense, put on a pedestal, where he is projecting qualities onto her which she simply does not have, and she feels pressured to meet these astounding expectations of a much older man that she can't possibly live up to.
In short, it could have easily been pretty messed up. Especially given the Trespasser revelations which stated he didn't really think she was a person at first.
The fact that Lavellan chases him is important. The fact that he isn't expecting anything of her - only to be caught off guard, is important. I don't really mind how feminine/masculine she is, because we sometimes imply those expressions of behaviour are more closely tied to power than she actually is.
The imbalance thing was a big sticking point for me, for a while.
I don't see Solas as the kind of person to put anyone on a pedastal, not even someone he loves. It doesn't seem in him to do that, which I like. If anything, he's so frequently surprised by people's better natures that even when he's trying to sincerely compliment them it often comes across as rather insulting. There's a banter where Cassandra says that for Solas to be 'surprised' by her so often, he must have a pretty low opinion of her. I shouted "thank you!" at the screen. As much as I like and love Solas, his condescension - intentional or not - was always profoundly irritating. There were times, such as when he calls Varric "Child of the Stone", that I kinda wanted to punch him. For most of the game though, I took it as a trait that made him more ... ah, not human, but fallible and relatable. So with the reveal at the end of DAI, my reaction was pretty intensely negative, not just because of the untruths, but because I had to adjust my view of everything that made Solas more "human" ... and find that he was now less so. And I don't know how I'm supposed to feel about inadvertantly romancing a god, but for me the reaction tends to 'ick'. There were already times when he says something 'nice' to the inquisitor in a way that made me feel like she should be getting a dog biscuit and a pat on the head, and that was bad enough. Now I *actually* had to ask myself if he even saw her as a person rather than an amusing pet. Which felt really disturbing. I replayed some of the scenes and chose to conclude that 1) Solas would not choose to use a person that way, and/or 2) he does in fact genuinely admire and care for the inquisitor ... though apparently not enough not to want to destroy her and everything she loves. Ugh. Must not start the spiral...
Anyway, I am grateful that, as you said, the relationship is for the most part presented as one of equals, at least enough that I can believe it was real. For a while - shortly after finding out who he is - I was feeling gross enough that I was ready to erase the romance from my headcanon.
But I didn't. I wonder how much I'll come to regret that in time. 