I just realised there's one more reason why I would like to use pure data API instead of specialized DSL. Just a nice and compact way to build data structures.
Because if you work with plots and data analysis, you probably spent at least 50% of the time with Python and/or JS/TS. And you don't want to learn and use 3 different plot libraries, with different syntaxes in those 3 languages. Vega-Lite again shine here. Because it has data-driven API. And the data - arrays, objects (maps/tables) etc. look pretty much the same in all languages. So you are able to use almost 1-to-1 ploting code in Nim, Python, TypeScript.