Honestly, I don't think that the average consumer out there knows exactly what cruise lines Carnival owns.
I think that the people who pay attention because they cruise frequently understand that the recent problems with Carnival could have happened to any other line (e.g. the recent fire on the Grandeur of the Seas) and those events will not make them switch brands. The people who don't pay attention wouldn't know to avoid the other Carnival owned lines.
Just my two cents.