It seems silly to have to use the overlays to color-code categories within the SAME calendar.

Desktop Outlook lets users color-code by selecting the event and, choosing "categorize" from the ribbon. In SharePoint, they have to create separate filtered views for each category and then overlay them, which seems needlessly complicated by comparison.

Overlay should still be used for layering SEPERATE calendars (as in Outlook), but it shouldn't be necessary just to use categories already defined within a single calendar.