They are us, though. There’s no eukaryotes without mitochondria at all. We are part prokaryote in every cell, apart from the equal number of fully prokaryotic cells in our various microbiomes. Hence the term
holobiont for animals like us. We’re pretty much a walking ecosystem.
In some ways, it’s wrong to imagine the branches of life are actually branches. Loki archea and alphaproteobacter together gave us the last eukaryotic common ancestor, and then bacteria continued to live around and in eukaryotes.
That said, mitochondria can’t be called prokaryotes within us. They’ve given up too many genes, and can’t survive on their own.
Of course, the rest of us can’t survive without them either, so it’s a complete mutual situation.