Avira, I absolutely agree that people can, and should try to, do chesed in any job. This is under-rated. many Jews used to be in a situation where holding any job/business was necessary for survival. In our days, B’H, people have some choice and it makes sense to choose the one where you do more chesed (in addition to other considerations on how it affects your own life). So, indeed, possibly a good plumber is better than a bad doctor…
But in any case, one should probably maximize amount of chesed he does – she ein lachem shiur. It will look weird if someone helps an old lady cross the street and check off “did chesed today”. So, someone visiting a sick person is great, someone who visits ten – is better; someone who can actually operate on a sick person and heal him – even better; someone who invents a drug that helps thousands – even better. Not in a sense that one person is better than the other, but in a sense that if the same person can do more, he should do more.