In my head, I've worked out the rules for what Flight can carry while she is flying.

As we have seen, she can carry Snakey or Saber, but not effortlessly.

For any of the other adult characters, the best she could do is try slow their descent while falling, and even that isn't foolproof. Back when I was posting Chapter Ten, fans had pointed out that Flight could have left the City of Feta at any time, but if she did, she would have to leave the others behind. It would have been a pretty big hole in the plot if she could have just lowered the others over the wall, one at a time.

Basically, Flight has a potentially over-powered ability and I had to make sure there were strict limits to keep her from breaking the plot limitations. For example one of the reasons why I gave Flight wing-arms, instead of giving her separate wings on her back, is because I wanted to limit her ability to carry things while flying (the other reason is that wing-arms are more birdlike.) 

But, at the end of the day, it just makes more sense for Flight's type of bird-people to be more light and agile than strong and muscular.