I see Shadowheart as the evil one and if anything Lae'zel as the neutral one.
With respect this is where you are losing out by getting the impressions from the videos and not the game itself

I urge you get the game so your opinions have a greater chance of influencing the final product.
You are missing the moment to moment interactions the -- Shadowheart 'approves', Lae'zel disapproves pop ups. Anytime I talk my way out of conflict SH is happy and LZ isn't. SH tends to approve of expressions of kindness, LZ doesn't. When you save an innocent -- from a child to an owlbear cub you get "Shadowheart approves".
LZ is a perfect LE space nazi. (stole that)
Like you, I want alignment in the system and we both want an entirely good party. If someone wants to play with the equivalent of the core BG party they should be able to do so.
But I do like the battle for souls that I think I'm seeing. My guess is that SH was either a priest of Selune or one of the kids abducted by the Sharrans in the blighted village. We may even be wandering through the places where she was abducted. So yes, SH is neutral evil but having a crisis of faith -- does listen to her heart or to the teachings of her goddess? I'm hoping that she will look to the MC for "should I embrace Shar" or "should I return to Selune instead"
And, again, this echoes Viconia who is the one evil character who doesn't urge you to join with Bodhi, the one evil character who will save the beggar from prison etc. In fact the only evil act she approves of is turning into the slayer. She was a Sharran that becomes neutral.
And Wyll is clearly on a road to damnation but he refuses to take the evil path of the game and he wants nothing more than to be seen as hero. He's also walking tightrope and I hope the devs let him fall either way (on our advice). His personal quest is to get out of the infernal deal he's trapped in -- which could come to a crisis point, will he give up that power and *be* good or will he let his vanity doom him. Right now I'd put him as Chaotic neutral, tending evil but redeemable.
Now I also want Mazzy Fentan. Granted there wasn't that much to Mazzy but I loved everything we got. Just a good person who is out to fight evil, make the world a better place and enjoy some adventures. So sick of the continuum of video games that only have a continuum from edgelord to yet another "grey" chacter who understands that morality is subjective and people are just mix.