Trying to estimate the impact one can make is OK thing to do, but I comment here just the article and how I see it. So I've now moved to the part 3 of the article, let's see the conclusion:
"I think my 17-year-old self would find that pretty galling. He’d signed up to medicine to save loads of lives, and he’d find it a bit of a downer to see this his entire medical career would likely do as much good as a £10 000 donation to the right charity. But that would be the wrong way of looking at things: instead, he should see that saving 17 lives is a vast amount of good, and being able to do 30 times more good on top of that is awesome."
Well... sounds a bit better. But the whole series still looks more like an excuse for somebody to forgo his medical career (also from the Part 3):
"If I become willing to work as a doctor, then I increase the supply of doctors. If more people are willing to be doctors, then the NHS can slightly decrease the wages for doctors (1). If the wages are slightly lower, the budget can be used to hire slightly more doctors.
How this all balances out is studied by economists. If the labour market for doctors is in equilibrium, then increasing the supply of doctors by one doctor, will probably increase the number of doctors by about 0.6 (2)."
I'd like to know if the article author really grew up to be a doctor or if he's now some activist in some charity instead.
Take a look at what the site suggests as the "right careers" for impact after I've filled the "career guide":
1) Management consulting (for skill-building & earning to give)
2) Foundation grantmaker
3) Think tank research
4) Economics PhD
Well if the guys who end up on this position only know to count megadeaths and QALYs before, I really doubt they will even understand what they decide about. But they'll surely have some impact, if it's a good impact it's fully another question.