Now you could argue that tools to manage it are a feature.
Exactly, this is my point.
it's still just an aspect of the technology, not something that was designed by choice
I agree that this is an aspect of the technology. But it is also true that when you design and write the code, if you put code to freeze accounts you are adding this as a plus, as something specific for that blockchain, you could summarize it as a feature.
I understand that freezing accounts could happen in all blockchains, not specific ones. But you could label those blockchains in that way when the majority of miners/producers/witnesses decide to apply a specific code to do it.
btw, I liked your article. Good to see the history behind the decision of DPoS.