This may be a bit confusing but Vega only uses some D3 helpers, it does not generate D3 code at any point. See https://vega.github.io/vega/about/vega-and-d3/ ht

This may be a bit confusing but Vega only uses some D3 helpers, it does not generate D3 code at any point. See https://vega.github.io/vega/about/vega-and-d3/ https://vega.github.io/vega/about/vega-and-d3/ for details. But you high-level point is accurate, D3 is more expressive since you can use all of JavaScript.