I think she is just kinda the default if you have no imagination - softspoken human female that isn’t totally obnoxious.
In terms of female romance options Lae’zel is the only one who it seemed to make sense would be forward enough to try and jump your bones after just 2 or 3 days. Karlach wasn’t even an option for me, she had no romance adjacent dialogue at the tiefling party. I wonder if part of that was just how late she joined up in act 1, I did get her engine “fixed” for the first time but it was one of the last things I did and I can’t remember if it was before or after clearing the goblin camp.
I did really enjoy Shadowheart’s arc though, especially since I generally adopted a policy to not suggest or try to interfere with the companions’ quests. Just left them to their own decisions without trying to sway them, and the fact that Shadowheart chooses to reject Shar and Lae’zel chooses to reject Vlaakith (or at least hear Voss out) made for two of the most powerful moments in act 2 IMO. There is lots to like about all three of them throughout their arcs and that’s part of what makes them so great.
Same, I was averaging 5~10 fights per long rest by the end of the game because I was trying to efficiently swap people out depending on who was low on health or spells, or use whoever I thought would have the most relevant dialogue for the quest(s).
My default roster was usually either Shadowheart, Gale and Laezel or Karlach, Wyll and Astarion. I was playing an archer sniper ranger so I basically always had two melee, one caster blaster and me as DPS and CC through arrows. I actually really liked the arrow system to give bow users more utility and if I ever run a campaign I’d like to adopt that. I’d make them cheaper though.
I never got to actually use Halsin. I tried to swap him in several times and it just never worked, then he was killed via plot events in act 3 via a mechanism where I could not save him. I used Jaheira a bit in late act 3, just for the Harper & Minsc stuff, not much after that. Never used Minsc, too much overlap with me, Laezel and Karlach.
I found both Wyll and Gale pretty frustrating, but that’s likely because I was trying to be so conservative on rests.
Don’t know how people have already run through 3+ times, I spent like 150 hours on my first run and saw probably 85% of the game… also the ending was pretty disappointing. I’m not itching to dive back in but I’d be interested in DUrge as well as interacting with Minthara more.