I haven't seen a single post addressing these specific points the OP brought up. And no, I don't think answering these points with "this fight is avoidable" or "but you can exploit this and that in the environment" is satisfactory.
So just to be clear, we have one side who is screaming that the Homebrewed extra abilities that players have makes the game too easy, and you have another vocal group that says that the encounters are overpowered - myself I am fine with the balance but I would like to see some of the more exploitative stuff- that players have -removed or tightened up.
But so be it:
Spectator:Other posters have mentioned specific abilities which are helpful on these fights and party composition that is good for the encounter. I guess you didn't see those? I think Ragnarok mentioned a few that Lae'zel's Frightening strike was extremely effective as well as push attacks from Eldritch blast (Wyll), and Thunderwave(Gale). None of that is Homebrew btw. using potions is apparently homebrew despite being in the DMH so we will leave those out I guess.
Dissonant Whispers is amazing as a spell if you have a GOO lock. A Ranger or Astarion with two handed fighting or a ranged attack is great for hitting multiple drow to break the charm effect.
Shadowhearts Guiding Bolt OR Inflict Wounds upspelled to level 2 is a shocking level of damage, plus her divine channel ability to create a decoy is great for protecting the group by giving disadvantage on attacks against her and party members close by.
Personally at 800+ hours I have used every single party composition imaginable and beaten this encounter with just the abilities we had. Like other experienced players have said, I just don't even think its that challenging. And I don't use barrelmancy or throw people around or use mods.
Bullette -
Ok, this is a rough encounter. Again an optional one but still can go badly. I do agree that the Leap damage and the attack can be a bit much, at best you will lose a party member. The game tries to help you here by placing you in Turn Based mode which you should use to spread the party out and hide if you can.
After that you need to use Lae'zels Frightening Strike, and Shadowhearts Command:Halt abilities immediately and repeatedly.
The surprise issue: Surprise is bugged right now and the Duegar don't always start with surprise, nor do I think its intended that they start with surprise except under really unlucky circumstances. I think you have to see none of them (fail all perception checks) and try to access the boat. I am not 100% sure as while I have had a surprise round here, its not a typical occurrence.
