Even the minimal 'hello-world' Quick application, i.e., only a QML Window, can hit ~400MB in terms of its application package size. Digging into the package content, it is found that:
1. Many unnecessary plugins (~70MB). This can be solved by -no-plugins.
2. WAY too many unnecessary resources (~270 MB). I don't think a simple 'hello-world' requires Scene3D or Effects or Particles, etc.. But the files are copied to application package whatsoever.

I think macdeployqt can use some revision/improvement.