Well, to be fair, I know people and projects in the developing world, and buy things for (or give money to) people there too.
I've also seen the impact of organizations which promise to spend money to save people there, and it's not always pretty. You can't serve two causes well. Picking between Western donors and local recipients, successful NGOs must choose to serve the former and not the latter. That often just distorts markets and causes its own problems.
To be frank, with that attitude, we'd never make better decisions ever. We'd always see that things get complicated quick.
Things ARE complicated. Teams spend time navigating the questions and coming up with their best answers - the poster who started this thread posted a site that has done that exercise https://www.givingwhatwecan.org/giving-recommendations/
They have a model, and they can iterate on that model as they get new information or insights. It's hard for me to think that their model is worse than my lack of model.
Well, no. My claim is that donating to individuals doing work in the field is almost always a better path for individual donors than working through megacharities, or even through charity aggregators like this one.
For large-scale work of the type you describe, family foundations do a pretty good job. Gates, Schmidt, CZI, etc. all have exceptionally competent staffs who are able to take in grant applications, sort through those, and support quality projects in a way in which you or I can't. Program managers are top people in the field hired to rigorously evaluate projects.
They have billions of dollars to throw around too. If you want to fight malaria in Ghana, be Bill Gates. Or if it's something you're passionate about, take your next family vacation in Ghana, understand the people, context, and culture, and THEN donate to good people or organizations you know there. Combine your vacation with your giving.
What family foundations don't have are the cost structure to support individuals in the field or small organizations. If there is a good project in a school in Ghana, there is no way they are raising funding through Gates/CZI/Schmidt/etc. On the other hand, if you see a problem and spend money to fix it, you'll fix it. If you see an organization in need of resources and donate them, they'll have them. It's really not rocket science to do that.
I've also seen the impact of organizations which promise to spend money to save people there, and it's not always pretty. You can't serve two causes well. Picking between Western donors and local recipients, successful NGOs must choose to serve the former and not the latter. That often just distorts markets and causes its own problems.