'mewing' is my natural tongue posture, and i can confidently say that i have a better lower third than the majority of people i see IRL.. but i really doubt mewing is the reason.
It helps, but it doesn't give you any insane permanent effects if you're already done developing.
For a good experiment - try having the best tongue posture you can right now and hold it. The way your face looks is the way your face will look no matter if you mewed for 5 minutes or 5 years. All mewing does it get your tongue used to a good posture which instantly helps with your looks and breathing and doesn't do much past that. Mewing prevents bad looks (aka. mouth breather look), but doesn't GIVE YOU good looks, if you get what i mean.
However, if you're still growing and developing (like anywhere between 0 - 17 years old usually), you can see permanent effects with mewing, but it's usually nothing significant.
Still, it's a good QOL for breathing and health in general so you should be doing it no matter what.
Salludon got multiple surgeries done, it's been confirmed long ago.