Again you're oversimplying here.
You're telling me a person with low as fuck testosterone who eats XXXX calories a day and exerts XXXX calories is gonna have the same body composition as a person with high as fuck test with the exact same calories?(assuming age etc are the same as well)...........fuck no....The person with higher test/better genetics is gonna get down to the low bodyfat percentage easy as fuck, the person with lower testatorone is gonna struggle....So it actually does determine whether it not it could happen...Sure you could starve yourself to get shredded but you will be losing muscle mass, only a few people can naturally get super shredded and still keep decent muscle mass.....Not everybody can do that, it's completely dependent on genetics.
Again, for the normie, following the advice of "calories in/Calories out" is gonna make em lose weight.....but they aren't gonna get close to getting shredded/cut easily as you make it seem....They will get in shape, no doubt but they won't get to super low body fat percentages...it's honestly not natural for some people to be that shredded.
Lets use Kelvin as an example....Under a professional nutritionist, dolce, he was in the best shape of his life when he was making welterweight......Dude still wasn't cut, and im sure Dolce was trying to get him as lean as possible....it simply didn't happen(and if it could happen, it wouldn't be easy)....Calories in/Calories out still responded here, obviously Kelvin lost weight but he was no way near close low body fast percentages, and that's genetics....no way is it effort....Im sure Dulce does the same shit with plenty of other fighters, except the other fighters bodies actually get shredded since they respond better to less calories....Kelvin's body doesn't.
It's not healthy for people to walk with super low body fat percentages, some people can pull it off naturally...others can't, if Kelvin seriously tried to keep as much muscle mass as he could while losing as much body fat as he could....his hormones would be fucked up, it honestly wouldn't be that beneficial to him.......However other people's bodies are different and they can be super lean year around with no problems.
inb4 people claim he really is a lightweight so that's why he isn't lean lol.....even if he moved down to Lightweight, I'm sure his body composition will stay about the same or he would lose a shit ton a muscle to reach that unnatural state of leanness which wouldn't benefit him.
So yes you will lose fat....but how effectively/how much fat you lose while keeping muscle, is based on genetics....has nothing to do with will/trying...so how low bodyfat % you can get while keeping muscle, is largely determined by genetics.