Nearly 200 countries. But you also have to consider the countries that may have had benchmarks, but are no longer countries. That certainly is a possibility. So, theoretically, you could have more categories than countries. I doubt this is the case now, but very well could be in the future.
I guess you have to ask which would be better. One category with thousands (maybe millions?) of waymarks, or hundreds of categories with hundreds of waymarks each.
I prefer having more categories than one overall category (like Benchmarks instead of U.S. Benchmarks, U.K. and Ireland Trigpoints, etc.). This makes it easier for those who want to find specific things. Sure you run the risk of having a lot of categories, but I think that is just going to be inevitable in some areas (benchmarks, historical markers, anything cemetery related).