I've heard climate scientists that describe climate change as a "more energy in the system" phenomenon. The overall system for now is mostly the same, but every event inside of it has "more energy" than it had before.
For hurricanes this seems especially problematic because the historical categorization system is based on radar-observed width of the storm. "More energy" means that the categories stay the same over time, but every category is getting worse (more rainfall, heavier/faster winds, further travel, higher damage).
As with so many statistical phenomenon, it's also a reminder to be careful what metrics you are trying to compare. Comparing just the hurricane categories to historic values may just be the exact sort of wrong metric, for these "more energy" concerns.