Defensibility in AI does not come from the model. It comes from proprietary data that cannot be scraped, workflows that regulators recognise, and switching costs created by compliance dependency.
Layer 3 has none of these by construction. Its inputs are public APIs, its outputs are commodity, and its customers can leave in an afternoon. Layer 1 has enormous barriers, but they are capital barriers — which means the winner is whoever has the cheapest balance sheet, not the best insight.
Layer 2 is the only layer where domain knowledge converts into structural advantage. The barrier is accreditation, data history and institutional trust: expensive in time, cheap in capital, and effectively impossible to shortcut.