Being manipulative evil can be a lot of fun when it's written correctly and the story supports it. I have played a lot of RPGs and unfortunately very few of them have anything remotely worth mentioning. The main one I am thinking of is Kotor1 and DA origins. What both of these have in common is that they are very linear and made my large studios...
I highly doubt Larian has the human resources to create a story that caters both to good and evil, when 90% of players play good characters, and those 10% who play evil characters will not go the extreme path anyway. It's one of my criticism of the evil MCs / companions. Astarion is not evil- he hides that he enjoys being the hero. Wyll- devils in 5th ed are not evil, some can be lawfully neutral. Shadowheart: utterly incompetent at being evil, knowing she has healing spells. Lazael: very easy to manipulate with honour, so a poor villian.
Why I recommend / suggest that Larian takes the rarely traveled path and fully commits to evil choices, I do not want small intensely evil moments with no pay offs. I would prefer few, highly evil and or sadistic options with large pay offs.
Eg
1): kotor: on manann you can choose to poison the ocean and kill a 100? year old shark, the result of doing so rids the universe of Kolto, and leads to 500M deaths in the battle between Vitate / Revan and Malak vs Republic. If you decide to embrace the evil nature of your actions you can torment the entirety of their race in court, get a ton of loot, and still be allowed to return (lawfully evil). I have never seen a game where you can do this.
2) kotor: on Kashyyk if you push out Czerka over 1K credits vibroblade out of greed, the result is a flat out war that lasts 80 years and leads to thousands of dead, 50 years of slavery, wookies mass genociding each other, and hundreds of people loosing their homes and families- all knowingly as your instructed on what will happen as a consequence of your actions. And it's beautiful.
The above are perfect examples of what kind of path or options I would personally prefer in BG3. I HOPE Larian will choose this route as making a handful truly memorable evil events is easier then a lot of none meaningful- still memberal events.
The NPCs in KOTOR weren't exactly competent at evil either. You really had to work on corrupting most of them (if you even could). Regarding choices, I'm pretty sure teaming up with an evil god's followers to slaughter a bunch of refugees counts as a pretty evil choice in regards to the reach of your character's capabilities. BG3 isn't set in a galactic war nor are you the single most powerful person in the universe as Revan was.
Scale is an important distinction. Besides, who knows how everything will pan out in the later acts. The trailers/teasers have hinted at being able to shut down an entire faction's guards before interacting with it's leader, which seems pretty large scale relatively speaking.
