I think most characters' prime directive is finding a cure to the tadpole in our head, if you want to make the evil path more compelling, draw more, and more clear, lines between how they might be able to provide that. It's something you have to do especially considering goblins are typically buffoonish opponents.
Also currently aligning yourself with the goblins requires, without some metagaming anyway, turning down your first clear lead (Halsin) and taking for granted that you're loyalty to the people responsible for your plight will reward you for siding with them, this in the context of having been implanted with a mind controlling brain parasite.
None of our evil characters seem too interested in joining the goblins, Astarion is intrigued by the Priestess Gut, but he's also the only guy so far who doesn't want our tadpole removed. I guess this is a long walk to arrive at a conclusion that I can only think of Chaotic Evil characters not being interested in finding a cure. Though I'm not sure how a non-gith Lae'zel would figure the pros and cons of joining the Absolute.
I've spoken a little bit about this, how choosing to help the grove doesn't mean you're good, because it still makes sense for a self-interested characters. This whole grove/goblin conflict should only interest good characters, people interested in intervening for the sake of others, for evil characters your questions about power and strength would presumably be secondary to your own self-preservation.
Edit: I saw this mentioned somewhere, but making us able to side with the goblins in the first fight would also be a serious improvement. Is that possible?
I would say evil is not a monoculture. There is the kind of evil that values self-preservation over everything else, but Githyanki are not like that. They are literally the type of evil that values strength and imposes those values on the multiverse. To a Githyanki, anyone who cannot impress them with their martial prowess and ability to defend themselves is just a future thrall they have to deal with. This informs their worldview and is key to their ability to survive in such an inimical environment.
