I think the correct understanding of the Halacha goes as follows.
The only reason we are allowed to go to the Doctor is because the Torah allows it (V’rapoh Y’rapeh)
Meaning, if you are feeling sick, you should not be going to the Doctor because Hashem has made you sick for a reason.
However, he does allow us to go to a Dr (I will attempt to explain why in another post, as I have understood from my teachers)
The Torah only allows us to go to the Dr for healing not for other reasons.
Therefore, cosmetic surgery would be a medical procedure that serves no health benefit and therefore Ossur according to the poskim.
Reb Moshe did not allow going to a Dr for cosmetic weight surgery (liposuction). This does nothing to help with health issues and is purely cosmetic.
Getting a ‘band’ around the stomach (or similar) is clearly a health benefit and the weight loss will help a person, lowering the risks of heart disease etc.
Does this Drashah make sense!
Good Night!