[semperdark]

You're not wrong. But over the enormous amount of time since, the "duplicate" organelles and systems needed for independent living were steadily carved out of mitochondria. While they do have their own DNA and replication process, the DNA is basically limited to specific things they need to perform their energy-generation functions and the replication happens when triggered by host cell replication.

It's a bit like if you took the heart from an animal and transplanted it into a human: is it meaningful to call it independently alive? Maybe, it depends what question you're trying to ask.