Microsoft makes money. The Bill & Melinda Gates Foundation spends money.
It's a bit strange to compare Mark Zuckerberg's money making organization to Bill Gate's money spending organization.
Pretty much all the research I've heard about social media indicates that it makes the world worse. So I think it is relevant.
Obviously a lot of people do in fact derive pleasure and some other benefits or they wouldn't keep using it.
That doesn't follow at all. When I used to use Facebook it was based on an addictive compulsion but each time I used I realized it made my mood worse. My life got better when I stopped using the platform.
Sure, but it could still be overall harmful. E.g. gambling, drugs, smoking.