Emma Watson is one of the most cited 'glow ups' of all time. I'm not sure where you're getting the idea she would've been hotter without braces, or how you could even judge that given the age she was in braces.
Take a look at those pictures and you can see how much better looking she was when she was younger. Look how her face is pushed in like somebody stepped on it after she has had braces.
People tend to confuse sexual maturity with attractiveness. You can usually tell how attractive someone is by the time they are 10 years old. Probably even younger. That's why all those Disney stars are recruited so young and all end up being famous. You can tell who is going to be hot when they are older. The average person just doesn't know what to look for if they're not sexually attracted to the individual.
I think that is why orthodontists get away with what they do actually. Their average patients come in at 12 years old and leave at 15 years old. The 12 year old was usually a lot better looking, but once you turn 15 you're sexually mature and and that gets people excited all on their own. Average adult logic is wow I just realized I'd have sex with you it must be because you're teeth are straight. No it's because you grew up the teeth have nothing to do with it but it masks the fact that you got uglier. If they actually looked closely at the before face they would see it's more classically beautiful.
I don't think Emma Watson would have been famous if she weren't recruited young. She is pretty average looking with the brace face. She got recognized young for being super pretty, got uglier with braces, but was already in the industry and "good enough" to make it work. You only need to have above average looks to be famous and the rest is intelligence.
I mean I just took another look at that before picture and her face is just perfect. Her teeth are great. A perfect fit for her face. Whoever decided to do that to her ought to be put in jail because she would have to have been one of the prettiest girls ever. It makes me so sad.