Hi,
from my personal point of view, a plug-in should not handle MIDI-CC at all. It’s the responsibility for the host to map input events to parameter changes. The host knows what external hardware is connected and which routings are active. A plug-in does not have the knowledge about this.
As a plus point, the plug-in does not need to make any changes to support the forthcoming MIDI 2.0 spec.
Cheers,
Arne