[CharlieDigital]

The opposite is probably true. Because you're gluing pieces together, the natural injection point for mocks is precisely where you would apply the glue.

A practical example is that my team is building a product that has a workflow which scrapes websites and then converts the output to internal models (before more processing occurs). The way we make this TDD is by simply loading static "fixtures" during testing instead of actually reaching out to the website to grab the HTML.

You might make the case "what if the HTML DOM changes at the origin"?

That's not the point of the unit test; the unit test is only testing "given this structure, this is the output I would extract from the HTML". If the HTML structure at the source changes, that's an integration or E2E test.