If Elriel was endgame, I imagine their first fight wouldn't take long to happen precisely because Azriel treats Elain like she's made of porcelain and she WANTS to be more active, in the ic.
It's really cute when a man is protective of his woman in romance novels, modern, historical, etc... Even in fantasy books, but there comes a point where you just tell him to go to hell.
It's a fantasy story, you WANT TO READ the fantasy part, the dangers, the training, the girl becoming strong. Feyre, for example, has several moments of Rhysand protecting her, and on the same scale, he encourages her to fight, praising her achievements, even facing the Weaver alone.
Now imagine Azriel who simply doesn't let her do anything? The most he did was lend her the TT, and he didn't even congratulate Elain for stabbing the King of Hybern, Lucien did that.
And given that Elain said she's not a child to be fought over, it definitely wouldn't take long for them to argue about it.
Now we have Elucien/Gwynriel. Lucien recognized that it was Elain who killed the King of Hybern. He crossed the battlefield to find her and see if she was alright. He volunteered to look for Vassa alone. Azriel TRAINED Gwyn, watched her with encouragement, encouraged her to cut the ribbon, her siphons and shadows reacted immediately when Cassian mentioned that something might have happened to her in the Blood Rite, a reaction he didn't even have for Nesta, canonically one of the people Azriel likes the most.
I never saw Lucien saying that Elain wouldn't do anything to risk herself, it was Azriel who did that. He doesn't have a "middle ground" with Elain. He doesn't protect her and encourage her to be stronger and more active in the IC, quite the opposite, he simply treats her as if she were made of porcelain, even though Elain herself has already shown that she doesn't like that.
And one of the biggest lies that Elriels tell is that this isn't a problem, that there's absolutely no problem with him just being protective of her.
It really wouldn't be a problem if you weren't hypocritical and didn't make several arts of Azriel training Elain. (Beautiful art, by the way, but you know. One thing or another, right?), Even you want to see Elain being more active, facing dangers, being a good fighter like her sisters, not being this "helpless damsel". And if it depends on Azriel, these arts will never happen.