It certainly is debatable. The 80,000 Hours folks have put a lot of thought into the debate. Yes, we can think of cases where it's better to use your career to help directly (e.g. I'm glad Jonas Salk was working on vaccine development and not, say, banking). But for most people, I suspect earning to give is a more helpful option than whatever they could contribute directly.

I assume you're referring to Gates. He may well have done more harm than good, since I understand the intellectual property laws pushed for software have been applied to medicines. But Gates seems to have had the initial goal of financial profit and only later turned to altruism. If your goal is altruism all along, you could run a company so as to foster good regardless of profit. Google seems to be a company that's financially successful but runs many side projects that are altruistic rather than profitable.