The one piece of evidence that I think supports Sebastian not being a romance is the fact that this game has a romance achievement but Sebastian's romance doesn't unlock it. Otherwise, he's a romance. Just because he is a chaste romance with less content doesn't mean he's not one.
Eh, achievements are meaningless to me in this regard, don't really care if a character grants it or not. Him not granting it isn't really a reason to not consider him a romantic option, he's just a different romantic option (clarifying here that I DO consider him a romance).
But imo, Tallis is just as fulfilling in that regard (more so actually), even if its just a series of flirts that doesn't technically lead anywhere (it could do so in the future if we go by certain info elsewhere...). Besides for many people a chaste romance is just as unfilfilling anyway.
So err, I'm sticking with my assessement that DA2 was technically even in regards to the LI ratio.
Not like it really matters to me anyway, all I care about is good options, not fairness.