Mitochondria have about as much in common with bacteria as apples do with oranges.
Interesting that those espousing these theories of endosymbiosis do not look at the differences between bacteria and mitochondria or chloroplasts. What about just for instance, the presence of two very specialized membranes in the organelles whereas bacterial membrane is single and also very specialized, but very different from the organelles. While neither I nor anyone else on this planet has a clue yet why mitochondria make a few proteins on their own, the answer may lie in the specialized nature of these proteins. Most of them form subunits of larger polymeric proteins, whose other subunits are cytoplasmic proteins encoded for in the cell nucleus. Without, for the moment worrying about how such a feature could be orchestrated between an endosymbiont and its host, lets look at what is involved in getting these cytoplamic components into the mitochondrion.