Except it would make no difference because you find in Act 2 that half the tieflings get caught, tortured, and killed by Absolute cultists and the Drider in Act 2, and Zevlor is spirited away. So you know, Minthara, the cultist you helped along the goblins, that same faction you teamed up with kills the tieflings even if they managed to escape the Grove. So it absolutely makes sense that good aligned characters leave your party when you team up with a ruthless, evil drow paladin who sees people only as tools to be wielded for power. Karlach was literally sold to hell for power by Gortash, and Wyll has been a slave to power. I don't know how you expect them to turn on their morals just so you can be evil and ruthless and still have access to their story. It's almost like people don't want negative consequences for choosing evil. Your reward is you get to see the game from the villain's perspective and get the most unique follower race and best class follower, a drow paladin whereas good playthroughs don't have a single drow character and it's all humans and vanilla elves with the exception of Karlach. You also get Halsin as a druid, but druid is a trash class so you will probably respec him to something else. Good players also get another trash class in Jaheira as another mediocre druid, and then Minsc as a trash 2H ranger with no good supporting stat block to play him efficiently unless you respec him to rogue or barb/fighter, and by the time you get to recruit Minsc the game is basically next to over, so he's a wasted character.
I am not clear what you definition of the term "no difference" is, but having played through act 2, this is clearly inaccurate. Several chapter 2 side quests are related to Tieflings, with obvious follow up indicated with respect to Dammon, Zevlor and Mol at least. And obviously the loss of Karlach and Wyll is a big deal. Given an inaccurate account of chapter 2, I am not confident in your account of chapter 3 either.
As for Karlach and Wyll leaving if you team up with the Drow, again, this could be a persuasion check like persuading some party members to use the tadpole. You could argue it is necessary to infiltrate the cult. Additionally, whatever the plausibility, it is a damn sight more plausible if you haven't killed off the Tieflings that Wyll was actively assisting and with Karlach herself being a Tiefling. The druids are lead by Kagha, who is hardly a very sympathetic character and not taking her side is hardly the most unequivocally evil thing you can do. If the position is "we got the tieflings out and its a shame about the druids, but there were going to lock themselves away and offer no help; we might get somewhere if we work with Minthara", yes its a bit iffy, but I can see Karlach and Wyll both accepting that. And frankly, there are plenty of in game actions you could argue should result in certain party members leaving which don't.
And no, I don't want evil choices to be free of consequences. Not getting Haslin is fine. Not getting access to certain items of quests is fine. What is not fine is the massive NET loss of content without meaningful upside. You go from 6 to 4 party members for half of chapter 1 and most of chapter 2. You lose a lot of quests, experience, items and so on. What is the upside? I would have no issue with these loses if comparable upsides were offered, but this plainly is not the case. And far more realistic than expecting Larian to add a lot of additional content to what, lets be honest, is an option most people wont take, they can work with what they already have. Allowing the Tieflings to escape would be comparatively little work. It would still be consequential (no Haslin, no future interactions with druids), but it would not be a clearly inferior choice. If Larian wants to add in evil specific content comparable to the content you lose from siding with Minthara, great. But there is no likelihood of this actually happening, and that being the case, the best way to make this option less unambiguously the wrong choice is to not strip away as much content unnecessarily.
As for drow paladin, firstly, no its not all humans except Karlach. Laezel is a gith, shadowheart and half elf, Halsin an elf and Astarion both an elf and vampire. So of 6 origin characters, 2 are human. Again, you are just getting basic facts wrong. Secondly, what does having a drow in your party, or Minthara specifically, actually add to the experience? I have played using minor illusion for drow on my main character in the underdark and goblin camp where this is a fair amount of reactivity, but you have to be the one speaking and frankly, most of the difference is pretty superficial and it only matters for the person actually doing the talking. So unless Minthara has a boat load of character specific content (and apparently, she doesnt), who cares.
As for the evil perspective, again, what difference does this make? You can still interact peacefully with the absolute in chapter 2 if you side with the druids, up until you kill Kethric, so no significant change there. And there is no significant difference in how either the mountain pass, underdark and shadow-cursed land plays out, other than losing a lot of content in the latter.
As for paladin, you can respec in this game. Even if you want to keep it thematically consistent, there is no reason why you cannot make Wyll a warlock paladin (works mechanically and narratively) or even Shadowheart a full paladin (honestly, she is more zealous than wise, so arguably it makes more sense). Or just play a paladin yourself. Halsin offers you a class you don't otherwise get also and narratively, making any of the origin classes a druid really makes less sense than making Wyll or Shadowheart a paladin.
