It compiles into Echarts, but echarts already has a JSON co figuration spec

It's more like a simple high-level spec to make it easier. The idea is that you don't have to fill position / axes details just to make the chart work. The compiler has a bit of magic of using semantic types to optimize what parameters will be set in ECharts.

In some composite chart examples, the good-looking echart spec is like 5x longer than the simple Flint one!