When generating resources to binary files, QML files contained in QRC files are not compressed in any way. You can open an rcc file in a text editor and view the QML files in all their glory. When using rcc normally and create qrc_*.cpp files the qml content is somewhat more hidden in a long sequence of escaped characters (even if they are only literally the characters from the QML file listed as comma delimited escaped hex numbers representing those characters).

Using the rcc compress option makes no difference - QML files are not compressed within .rcc files.