As of Ver 16 we still have the problem that Events will not show up on a calendar unless you allow all your "To Do'" to show up as well. This is certainly not logical. Most users of Act will filter their calendars to exclude Calls & To-Dos to reduce the clutter.
Since there is already a switch to display events or not that should be all that is needed. If it is a limitation of the architecture then at least change it from To-Do to Appointment which is a useless Activity anyway.