Only conceptually, so to speak, as you can have both on… but how can a Component be opaque and draw anywhere on screen? It would really mean only the lowest Component in the hierarchy could be seen if we really enforced the rule of “fill the entire clip region if you’re marking yourself opaque” 
You’ll run into the issue that you’re seeing, for one. Also seen here:
And on top of that there will actually be unnecessary clipping because JUCE isn’t checking the “unclipped painting” flag of siblings when drawing each child. So excludeClipRegion() is still used for all these component bounds, even though the components aren’t clipping anyway when they draw themselves: