I'm legitimately curious how Abstract Algebra relates here. I thought that was all about group theory and such.
Lots of math but the models were shit
Mkay, but, this doesn't mean math is wrong. It means actual research is needed. Trials and case studies and comparative analysis and so on. Fortunately, that's exactly what givewell does. You can criticize Gates for not predicting second and third order consequences, but I'd argue the only thing we can do in the world where the higher-order consequences are somewhat predictable in advance is preserving the status quo.
The misuse of mosquito nets for fishing is bad, yes -- and depressingly ironic -- but you should check out the Against Malaria Foundation's response, where they say basically the misuse of malaria nets is not very widespread.