Description of problem: --defaults is global --optional is per-group only. This may not be a bug, but I found it confusing.
Would you also like a global --optional and a per-group --default option? The thing that might be a bit confusing here is that %packages --default is the same as clicking Next on the package selection screen, while just listing the group gets you its default package set.
Yeah, once I understood that it's not the same thing, it made more sense.