system
A chat on 4chan
human
This isn't wrong; comes down to the question of 'if a placebo works, is it effective?' 
 
However, there's a lot of things to know about subliminals, OP. 
Firstly, be wary - TikTok gen z 12 year olds found them and have made the majority of conversations around subliminals cancerously bad and not realistic whatsoever. Most are preteens that note any puberty-related changes as results; some are just delusional with no results. Check Reddit to see what I mean, it's a good laugh. 
However, subliminals are not new. They were a trend around bodybuilding forums and parts of 4chan around ca. 2009-2012, along with self-hypnosis. And the idea of it can be approached methodically. I can vouch it brings results - scoured a lot of those boards back then. But like hypnosis, it depends on how open to suggestion you are. 
In the most realistic, down-to-earth perspective, subliminals are basically a 'Power of Suggestion' hack. The idea is disguising affirmations within audio (or visuals in video) bypass the more questioning, skeptical conscious mind allowing you to make affirmations much more effectively. Cults will deprive people of sleep for the same effect, but for nefarious reasons. 
So if you were to say, give yourself subliminals affirming that you sleep very soundly, or are a confident person - yes so long as you don't have a hyper-un-suggestive mind, they can work quite well.

Going into the less-grounded but more interesting realm of subliminals, as you said some say you can use your subconscious mind to alter gene expression. Changing eye color, jawline, height, etc. There's some potential truth to this, which I'll note, but most is either misinterpreted or just plain untrue. 
Possible truths: White individuals with brown but not dark brown eyes, have documented and claimed some ability to change eye color. A lot of these are fake, but I found about 2-4 that I couldn't write off as such due to how well they were documented.
gpt
Those few also seemed to be consistent with each other. Meaning they didn't have some dramatic change like brown to blue. But brown to lighter honey brown, or brown to hazel. Each of them had their melanin visibly and slowly over the course of 6 months - 2 years 'unravel' starting from the outer iris inward. Very interesting. Seemed to only happen with the type of people who'd experience eye color change due to aging, but with subliminals, at an unreasonably fast pace (which, if true, hints at gene expression).
I've also seen some on bodybuilding forums change how/where their fat gets deposited; experimenting with subliminals without changing diet/workout/etc. for consistency. Results seemed to vary, but a few were abnormally drastic. Again, this was over the course of well over 6 months. 
Definite untruths: Most of the things you pointed out. Some like weight loss can come down to the positive affirmations influencing behaviors and the person just isn't associating it that way. But 'true' subliminals that target gene expression don't go with 'Perfect doll face' because they're instead targeting...genes. For example the fat distribution one from what I remember was a subliminal regarding white vs brown fat in the body, not 'perfect waist.' This seems to be from the newer TiKTok crowd.
human
I'd say if you have an open mind, there's really nothing to lose in trying out those types of subliminals. I'm currently experimenting; I'm also not as gung-ho about it doing anything and am just genuinely curious (I skeptically consider whether it could be possible if simulation theory is correct, which would make a 'hacked' subconscious a little less ridiculous). But again, I wouldn't even bother with most you see on YouTube or wherever; you either need to make your own or dig for ones not made for horny depressed preteens hoping to become a vampire. 
Lastly, some essentially argue Law of Attraction: 'Successful career' 'Make your crush fall in love with you' 'Everyone finds you charming.' I guess how you view these depends on how you view the Law of Attraction; personally I think most of it is confirmation bias/results of boosted confidence, so I put these in the same category as 'positive affirmations' and expect results along the same line - i.e., nothing incredible, but potentially beneficial to many.
gpt
One last thing to add - with subliminals, there are a few types. I'll only refer to the audio types. 1) hidden verbal affirmations, like you described, which seem to be most popular right now and 2) frequencies/tones, which was much more popular a decade ago. I can't say which is more effective, I think it depends on the person and purpose.