I understand in the case where custom behavior is required, e.g. an elaborately constructed and operated QGraphicsScene for example, subclassing the QObject in question is something of a no-brainer reasonable course of action.
However, what if you want to subclass simply for the purpose of code cleanliness. For example, if I have a QDockWidget that requires say dozens of widgets and layouts to be added to it, I can certainly create the QDockWidget first and then execute all of the code on that instance necessary to gussy it up. Or, I could also provide all of that UI build code inside of a subclassed QDockWidget instance, so that in the main application code I simply need to only create an instance of my "custom" QDockWidget and move on. This makes the main application code much cleaner.
Is this a misuse of the purpose of subclassing?
Definitely, it's not a misuse!
Logically, subclassing is intended to be used to extend/manipulate the functionality of the inherited class.
So, you are doing it right.
When is it Pythonic/good practice to subclass in Qt