Just to add to your thoughts:
- He says that this is an exchange of favors for helping save the grove.
- Halsin states that the tadpoles are an abomination and nature can't heal it by itself so he needs to protect it
- He's spent almost a third of his life in one place leading a grove instead of being "restless and roaming." And frankly, he's not good at it, although he is more harsh on his own performance than perhaps is deserved.
- He feels responsible for the shadow curse -- again, he is feels more responsible than he deserves. He feels he has delayed long enough addressing it.
- If you are playing Dark Urge, he is very protective of you when you confess your urges
Halsin's character has a number of issues, but I don't think this is one of them.
I am always confused when people say Jaheira overshadows him. If you want to play with a druid, you already have one set up? Jaheira is mostly a vehicle to find Minsc, who has even less content. By default she is spec'd terribly for 5e rules. Fan service, I guess, but so are Halsin and Minsc.
