For Dragon Age, I don't recall being able to make any character forsake their religious beliefs for a romance.
I said "change". You know, the entire point of rivalmancing in DA2, and of hardening/softening Leliana and Alistair in DA:O. I didn't say "religious change" specifically.
And how often, really, do BioWare romance arcs, or even BioWare character relationship arcs, push the player into changing an opinion or a belief rather than forcing the NPC to "develop"? Most of the time, the characters exist for the player to mold: player-character as God-Arbiter of All the Feels. It can get preposterous to the extent that some people on this forum have suggested that many companions have severe psychological dependency issues. But a lot of players want that fantasy of being able to determine everything about their world, and when they can't make it work how they want it to, they respond badly. Everything from character sexualities and opinions, to political realities in the game world, to the color and cut of their character's clothes.
For a lot of these people, there are only two kinds of game. They would describe them as "games that let me make choices that matter" and "railroads"; I would describe them as "godlike power fantasies" and "slightly more realistic depictions of individual choice".
It's problematic because Sera got into the relationship knowing Lavellan was Dalish, and now expects her love interest to suddenly give up her religious beliefs or else their relationship is over.
First of all, "knowing Lavellan was Dalish" means basically nothing, because "being Dalish" and "being convinced of the reality of the Creators and of the Dalish explanation for their existence" are not the same thing. And, y'know, even if Sera did know that, it's an entirely different thing to be religious in that way in a world where it isn't relevant, and to be religious in that way in a world where holy balls these things are RIGHT IN FRONT OF ME. Maybe she thought she could deal with it, but when it was staring her in the face she was like nope nope nope.
But more importantly,
that isn't problematic either. Even if Sera knew the elfquisitor was super-elfy-Dalish when the relationship started, and even if that ended up being the reason that they broke up, how is that
bad? Again, wrestling over religious questions is a fairly common and normal reason for relationships to fall apart. It's just how things are.