It would be great if hierarchical chart types were available. Currently there's not a good way to represent hierarchical data outside of a TreeMap, but TreeMaps don't always work well (particularly for small datapoints). An ideal chart type would be the sunburst chart (nested pie/donut charts), as it can have multiple layers, hide a segment (and all children), and potentially zoom into child layers.
d3 (one of many variations): https://observablehq.com/@d3/zoomable-sunburst
Currently the shared tooltip's position gets in the way of actually seeing the current category's series, as well as hindering any attempts to click on any series behind the tooltip.
Ideally, the tooltip should form off to the side of the current category's visible/clickable elements, either dynamically based on room available, or statically based on configuration (top, bottom, left, right).