I do think there's an interesting discussion to be had about how Halsin, continuously, flees responsibility.

The most obvious example of this is in Act 1, when he decides to call for a new Arch Druid to handle the Grove while he goes with you to Moonrise Towers, but this can also be seen in Act 2 when he leaves the Shadow Cursed lands to accompany you to Baldur's Gate. While he did travel with you to find the Cult of the Absolute, his primary motivation in Act 2 was lifting the Shadow Curse and freeing Thaniel. Regardless of how you resolved events in Act 2, it makes the most sense for Halsin to stay behind - either to help the land heal in the aftermath of the Shadow Curse, or to find a new way to free the land if you don't lift the curse.

But again he flees, and he goes with you.

Now I know the Doylist reasoning for this is Larian made him romancable last-minute and so handwaved in an explanation of Halsin wanting to tag along to help you fight the Netherbrain/he was dtf by that point, but the thing is it is consistent with his character. For someone who is continuously placed in a position of authority, Halsin seems to be deeply uncomfortable with responsibility - or at the very least feels deeply inadequate for the task, and all-too readily passes it over to someone he feels is more prepared for it.

By the epilogue he seems to have (mostly) figured out this part of his character, as he's returned to the SCL and is mentoring children there, but I think it's a shame we don't see this aspect explored more, especially since his content is so lacking in Act 3. If you're not romancing Halsin, he's just sort of...there. He has a few comments about Baldur's Gate and there's a few discussions you can have with him about civilization vs nature (which don't really go anywhere or have any meaningful impact on his character), but otherwise his character severely stagnates in Act 3.

Exploring how Halsin feels now that his greatest "failure" - the Shadow Curse - has been resolved, could have been a fascinating turn for his character. Forcing him to examine how that event affected how he views any other responsibility he's been given (It's easy to draw a line from "he feels he failed massively when Ketheric Thorm cast the Shadow Cures" to "he feels like he is incapable of handling any sort of responsibility") and helping him to reconcile those feelings could have been a really nice resolution to character threads that otherwise just sort of fall to the wayside by Act 3.

I just think there's ample opportunity for Halsin to have a really interesting character arc by Act 3.