Well, I don't want to spoil the party. I would love for Shadowheart to have more content, but it's essential to understand that both SH and Astarion are the characters with the MOST content in the game. I understand that they even made statistics where Astarion led the list followed by SH.
The thing is, Astarion and SH have two versions of their respective characters with tons of new dialogues and "romantic" interactions (something no other character has). The issue is that since most of us almost always choose Selunite Shadowheart and spawn Astarion, that's probably why it seems like there's so little.
If you ask me, I would prefer if they better divided the paths for SH so they have different reactions to scenarios with Mizora/Halsin, etc. Even so, I agree that they should add a bit more romantic content for Shadowheart in Act 2. The wait to see any romantic interaction between her and Tav becomes eternal, and what's there is not worth the wait when compared to Astarion's, where you have a long conversation in the camp with a hug included.
