The larger problem is that humans are kinda shit at eyeballing the relative size of areas. You can generally tell if one is larger than the other, most people just can't estimate how much larger one area is to another with any sort of accuracy (which is why area comparison graphs are often used when it's desirable to minimize the perceived differences).

This fixes the main problem, but:

Treemaps are indifferent to "unknown" or "unlabeled" nodes. Area is disk space.

Whereas the simple act of labelling a node adds another outer ring arc to the sunburst (thus more coloured area), even though the underlying truth hasn't changed.