Indeed, variety is, you're quite right.
Each to their own, if everyone liked the same things in women then we'd be in short supply!
I think that there is a decent range of variety in this game. From Mia, in ascending order to Lily, Robin, then Noreia. They each have progressively bigger tits, but all are realistic, not behemoths.
I think calling the 3 other girls' breasts in this "non-existent" is wildly off the mark, though.
Robin's are smaller than Noreia's, granted. But they are still a decent size. Not what I'd consider small, by any stretch.
Lilly's are smaller, again. But totally existent.
Not flat, or small, really.
Mia's are definitely small, but I think they're absolutely fine & appropriate for her frame size. Being so petite, she'd look pretty ridiculous with bigger, to be fair.
As for Twisted World, I don't know which 2 are the characters you refer to, but just about every female character visible in the screenshots is balloon titted & ridiculously oversized, exactly what the dev said he didn't want in the post I quoted for you.
The only 2 who are not, look similar in size to Mia.