Activity manager and virtual desktop widget both in panel

They do different things though, the activity thingy lets you switch activities whereas the desktop one makes the current desktop the foreground window. I never liked the desktop plasmoid much, perhaps replacing it with the one that opens the dashboard (i.e. ctrl-f12) would make more sense, then both would have a unified focus on plasma workspaces (i.e. the paradigm that is > boring desktop)

From an end user perspective, what's the difference?

The only use of activities I've seen that made any sense was on plasma-netbook. It looks a lot like switching to a different desktop. The only difference is that it's a different kind of 'desktop'.

I think having them both is confusing for users. It confuses me and I'm supposed to understand this stuff, at least a little.

FWIW, I am not even sure where the activity stuff comes from as our script does not add it ... there must be some weird script result overloading going on ... spooky.

The widget is injected by addShowActivitiesManagerPlasmoid.js via the update feature. Could probably be overloaded by an empty file via KDS.