Treemaps are very powerful during the data crunching phase, but they are not ok for a final deliverable, as they ask way too much to the reader's brain to get understood.
Makes sense. I'm curious though, do you mean that even with the same number of categories for each it's too difficult? ie. instead of using hierarchical groupings and all categories no matter how small, use only the top ~10 and bucket the rest into "Other" similarly to a pie chart or bar.