I'm new to this, but it seems like keying attributes you exposed in your HDA don't take effect. They retain the first value through out the timeline. Is this correct or am I missing something?

You need to switch to Evaluation Mode to DG in your Animation Prefs.

Unfortunately, when using evaluation manager, dirtying is only supported for the parent compound attribute, and our parm structure historically puts all the parm attributes in one compound. Updating all the parms if one parm is dirtied is a significant performance hit. If we don't want to break backward compatibility for the asset node, we could look at maintaining our own dirtying mechanism for the parms.