In order to make the evil path have substance, it needs to establish a proper motive and goal for our party. Whether that is more answers and true insight from a real follower of the Absolute, deeper infiltration into the Absolute circle, the possibility to join the Absolute willingly, a quicker and safer way to Moonrise or even power itself ... For me the only true reward for an evil path would be getting Minthara as a true companion with full romance, as compensation for Wyll leaving. I found her romance to be very sweet, especially with her wishing to take us as a consort to Menzoberranzan and belonging to each other for eternity.
You and I clearly have very different definitions of sweet, but otherwise I agree there's a significant gap in the game's recognition of and ability to roleplay different flavours of the side-with-goblins path, and I hope that's going to get fleshed out in the full release.
As you point out, there are various possible reasons why you might (pretend to) side with Minthara, and I'd suggest infiltrating the cult is one of the most promising paths. You may already know from talking to Nettie that Halsin doesn't really know what's going on, so whether he can help is doubtful and getting in with the cult may seem like a safer bet. Even though the True Souls you meet are unaware of their tadpoles, it's not unreasonable to think that if you can make your way deeper into the heart of the conspiracy then eventually you'll find someone in on the secret.
I disagree with RagnarokCzD that infiltrating the cult of the Absolute (which may later turn into joining the cult of the Absolute) shouldn't be recognised as a genuine path, and would prefer it were recognised in the journal as you start to find out more about the cult and its connection with the tadpoles, along with finding Halsin or the githyanki creche and all the other dead ends. Plus it would be good to have a level of confidence that this was a fleshed out option in the game - it's one thing to take a risk on a course of action that may not play out because of in-world factors, it's another to risk role playing an option that turns out not to be available or satisfying because it hasn't been written.
I'd also like to be able to discuss my rationale with my companions and hear what they think of it, good or bad. I wouldn't expect Wyll to decide to stick around no matter what the motivation for attacking the grove, but it would be good to be able to at least say to him or the others that infiltrating the cult is your best bet or give any of the other possible reasons why you may have done it. To Shadowheart, the closest I could get was to tell her we needed to clear the way forward, which isn't really the same. I think it was only Volo to whom I could say that I needed to gain the cult's trust (and, by the way, I'm not generally a Volo fan, but I think his speech to an MC who has betrayed the grove is *excellent* and cut me to the quick).
Others have already pointed out that agreeing to support Minthara seems to come out of the blue, and could do with a bit more build up. And we should at least have the opportunity to ask why she wants the grove destroyed - is it the tieflings, the druids, or both that they want dead? Is there something at the grove they're trying to find? Is it Halsin, and they don't realise he's the bear in their dungeon?
I'd also have found it more satisfying to have had the opportunity to deceive Minthara into believing I was on her side, and also that I was "hers" in the romance scene afterwards which my main character definitely wasn't. Her tadpole should give her some opportunity of spotting your insincerity, and choosing a deception option would have a different feel to me as a player even if, on success, the outcome was the same as just joining her.
In my playthrough, I was also trying to roleplay a character who wanted to infiltrate the cult but also undermine them at every turn where he wouldn't be discovered. He killed Gut, poisoned the goblins in the courtyard, subverted the spiders in the pit, and even freed Halsin, but it's not clear that any of that made any difference to the fight at the grove or anything else. He was doing this for Lolth, but I can imagine a neutral or even at a push a chaotic good character making similar choices in the belief this is the best and only way to bring down those responsible for the attacks on the Sword Coast and regretfully seeing the deaths of some innocents as being a price worth paying.
I'd also like there to be more nuance and complexity to the attack on the grove than just a wholesale slaughter. For example: the adult tieflings in Zorru's cave just throw themselves at you, instead some could attack to cover the retreat of others up the rockface and through the hatch where Lakrissa(?) is found earlier, and Minthara could send you after them giving you the opportunity to then let them go and deceive Minthara that they'd been too quick or to slaughter them. Or, if you know how to get into Mol's hideout, have the option to either tell the goblins how to get in or say you don't know. Or when going to deal with the druids, to give them the opportunity to complete the Rite of Thorns if they still have the idol and deceive Minthara that they'd already completed it when you got there. There would clearly be risks to leaving so many people alive with good reason to hate you, and there's a a good chance that tieflings would get killed in the wilderness anyway. But I'd like the opportunity either to reinforce my characters evil-ness by repeatedly choosing to kill people, or mitigate at least some of the impact of my pragmatic decision to work with the cult.
I think it might have been in a different thread that someone said that in many cases, good or evil comes down to *why* you do things rather than simply what you do, so when it doesn't give you opportunity to roleplay the why of decisions the game is missing something really important. I'm not in favour of siding with the goblins being a clearly laid out "evil path" as such, I agree with RagnarokCzD that would be boring and whether you do so or not there should be a branching set of options with different moral nuances. But whichever choice is made, the players should feel that the game is recognising their motivations as well as their actions. It could be that those motivations in the end don't make any difference, and that even a somewhat non-evil character who sides with the goblins to destroy the cult from within has to become increasingly morally compromised or fail. But if the game was exactly the same experience for that character as for someone who thought joining the Absolute for power was just a fantastic idea from the get-go, and all that roleplay had to be in our heads, I'd not find that satisfying at all.
