In my experience, it's still quite rare for floor singers and support to be better musically and professionally than the main act although it happens occasionally.

Of course, the main act may not always be our cup of tea and a good floor spot can be a welcome distraction. However, in most cases, floor singers would be unlikely to sustain the same level for a whole night...i.e. two 45 minute sets or whatever.

So all this "better than the main act" stuff isn't necessarily so unless it's a professional or regular performing act appearing while "off duty".