I know from my own writing that readers will often find themes I was completely unaware of and certainly had not planned. So when looking for themes I never assume the writer planned them deliberately. The writers may have planned them, or they may have discovered them as they went along and only sharpened up what had turned up by chance, or they may have just created themes by accident by repeatedly reusing ideas they like without any conscious awareness of it.

I actually suspect most Doctor Who themes will be unplanned and unconscious because they would probably be much clunkier and more even, but also more obvious, if they were planned and done deliberately. Overall I think it is fun to spot themes and patterns, but I personally wouldn't want to take it too seriously.