I believe that it's a common feature amongst a large portion of cults, but my scepticism arises at the use of it as a broad definition of what is or isn't one.

The same way you wouldn't say having a charismatic leader is the definition of what a cult is. It's certainly an aspect of most cults, but not the definition, nor unique to cults

That's okay. People have to draw lines to define things. I found the definition I provided above to be sufficient to my experience.