Small unit tests are valuable iff your small units are well designed and valuable. If they are brittle, temporary components they don't have much value, I agree

Small unit tests are valuable iff your small units are well designed and valuable. If they are brittle, temporary components they don't have much value, I agree, but writing mostly integration tests suffers from the combinatorial explosion problem and from making it hard to express succinctly what the important bit about a piece of code is (and besides, almost no test is 100% integrated, you always isolate something, even in full end-to-end tests). If you have many functional, stateless components, the unit tests can be particularly valuable. But I think many tests end up being badly written because people don't necessarily ask the fundamental question: "does this increase my confidence in the code?" I think that's the most important consideration when writing tests.