It's a fine line I have to walk, and I have to admit I'm still trying to find my own balance here. For every player who wants more "fluff", there are players who think there's too much of it. I want to give characters depth, but don't want people boredly clicking through things. A lot of it comes down to preference, but it's also something I definitely want to work on.
I've played some games where it feels like they're just padding things out with needless exposition. I'm huge on story (that's probably the only reason I play any games at all, these days), but there are quite a few lately that I feel belabour the point too much - looking at Danganronpa, Genshin Impact, and Final Fantasy XIV. There are times when less fluff is preferable to excessive.
Reflecting on this, I see the difference between my game and what those above games have done. They have huge casts of characters, and probably try to give too much time to all of them. Mythos, Book One, on the other hand, had a pretty big cast, but a very central story - trying to properly flesh out every one of them would have made it a bloated mess.
This is why Book Two is already going to have a decidedly smaller cast, but the same "scope" of a main story. The characters will get to have more personal moments, because there'll be fewer characters needing the moments.