Challenge in visualizing large coronavirus clusters in US data
How about a small multiples style visualization? A nice 2 x 3 grid would cover the six categories here. Size on X, frequency on Y.
This approach is one of the clearest ways to show this kind of data. The stacked histogram is difficult to interpret because the bars of the same color do not have common starting points. If you make six histograms arranged in a rectangle with common scale on the Y, you can quickly visualize the distribution for each category.
Here is a plot made with some simulated data like yours. The top image has all six categories on one plot, like yours. The bottom image facets each category into its own histogram with common scale. You can much more easily compare the six categories.