Currently, it is observed that Sunburst chart series data labels when shown, overlap or only the show/hide behavior of data labels can be achieved through the formatter function.

Refer the Sunburst chart's series data labels on the following link:- http://www.dundas.com/support/blog/sunburst-charts-homerun-or-groundout

Expected behavior is to configure the series data labels in such a way that if the arc size of a node is less than a particular value, instead of hiding the data label, show it outside the leaf level nodes of the chart, also adjust the distance of data labels and its connectors from the chart.