Personally I dont care about more body options at all. I utterly fail to see the gain.
Immersion and diversity aside, there are even some practical ones. Having normal or thin body while ALSO being tall (which is currently impossible) would provide a better scenes for romance with Karlach, for example

Immersion to me is a term that gets brutally abused all the time in gaming forums. A game has good immersion if it has good game mechanics. Thats the only trick to actually immerse people in a game. Thats why a game like chess has such extreme immersion.
Realism isnt one, unless lack of realism breaks your suspension of disbelief. The Tiefling and Githyanki both break my suspension of disbelief, for example, thats why I'm annoyed about them. No point in complaining though because neither will go away (or rather, made more realistic, like I would much prefer them), so whatever.
Immersion can be many things, but I'll tell you what it is to me. Dark room, noise cancelling headphones and a good RPG. I forget that this world even exists. I even forget that I exist.
When I play a strategy game I'm kind of half there. It takes focus, but I know that I am playing a game.
With BG3 it's kind of hard to forget this world when every woman in the game reminds me of filtered instagram bimbos, plastic surgery, nose jobs and lip fillers and the men aren't much better. Where are melancholic eyes? Smaller piercing eyes? Epicanthic fold on others besides the one asian face? Sure, there are a few more natural looking faces, but even those I don't like.
If a character has no personality it's kind of hard to roleplay them. Blank face ends up being a blank empty person. If I played BG3 right now I'd be only half there and my character's face (and her dopplegangers in the game world) would constantly remind me that I am, indeed, just playing a game. Sorry to say, but I expected more from BG3. Like I said before, I'll play it, but I'm no longer in any hurry and it remains to be seen if any improvements have been made by then.