I would argue cargo ships don’t need their own category in that case since they don’t exist for any other reason than to be part of the supply chain or other goods. All cargo ship pollution can be attributed to the cargo they’re transporting.
We don't need to eliminate categories, we just need to be clever in the way we present data. For example, there's nothing particularly difficult to understand in the statement "Cement is responsible for 8% of the world's CO2 emissions, half of which is from transportation, 1/3 of which is from cargo ships." If we likewise break down each category into its major sub-components, the sub-components can be recombined in different ways to produce a lot of interesting and actionable data. Having several charts side-by-side is much better than fighting over a single chart that doesn't add up to 100%.
0: https://www.sei.org/publications/shipping-emissions-per-comm...