Yoohyun would Not be a doctor
It makes sense for that to be his goal as a child since it's one of those jobs any kid knows makes a lot of money and is really impressive and good for society and such so Yoojin would have been excited for him as well and sure, he'd be great in medschool because he's really smart, but that also means he is smart enough to google, say, the average working hours of a doctor. And it's not even one of the jobs where you retire young. Which would both go against his primary priority of "spending as much time with hyung as physically possible while making enough money that he never has to worry about anything ever again." And then he'd just look for a different job that earns a lot Maybe he'd study computer science and fund a start-up that he sells for an insane sum before retiring with hyung to the countryside at 30. Or do air traffic control
And I think it's thematically relevant that he picked doctor specifically. He and Yoojin are two kids living in poverty and studying medicine is one of the few ways to escape that are not only respected in society but actually give him a level moral superioty. This makes it unique among options that promise a similar level of economic stability, like a law degree.
And obviously, Yoohyun does not give a fuck about morals or societal judgement. If he merely cared about the money he wouldn't hesitate to get into organised crime if he thought it paid. But Yoojin does care, so Yoohyun is trying to match what he imagines Yoojin's image of the Perfect Younger Brother is, which includes a medical degree. But it's clearly not something he has thought much about besides Yoojin liking the idea and there being money involved because as I said, the reality of being (and even just becoming) a medical doctor is opposed to what Yoohyun wants out of life: time with Yoojin.
He would continue to put a significant financial burden on Yoojin for the many, many years it takes to obtain that degree and then have to spend most of his life working.
I think in a no-dungeon au he would probably start med school, realise what it's actually all about, and then have the very hard conversation with Yoojin about what he actually wants and eventually drop out because Yoojin wants his brother to be happy.
The only world in which I see Yoohyun actually practising medicine full time is one where he never manages to drop his mask in front of Yoojin which I suppose is possible, but I like to think they would work it out even without a regression.

















