I removed all the categories from the single player missions. It's ultimately up to the scenario developer to explain what their scenario is about and to give downloaders some idea of what they are getting. Forcing the submitter to fill out extra fields and doing categorizing by mission size was tried in the past and it did not work out.
I think the best bet at this point is to use the tag system along with the description to let folks know what they are getting. I added tag suggestions to the single player category for single_tank, platoon, company, battalion, and brigade.