For what it's worth, I saw that someone else said that the Favorites order works as long as you don't scroll the screen to do it, so I tried that, and it seems to be true.
It's not a solution, but knowing that will certainly help at least some people be slightly less frustrated by this.
Basically, as long as you don't scroll while arranging Favorites, they'll behave.
If you don't have too many Favorites, and don't need to change the order very often, you can get all your Favorites where you want them, but it'll take a little longer to do it. You gotta, like, move the top one down just to the bottom of the screen, then move your screen down to where that one is at the top of the screen and then move it to where you want it (or to the bottom of the screen again, depending on how many Favorites you have and how many fit on one screen).
On my 6s, I have 7 or 8 Favorites on the screen at once, and 20 Favorites, so I'd have to move my top favorite 3 times to get it to the very bottom of the list. Not the best, but it's not the worst, and at least my Favorites are in the order I want them.