Isn’t there evidence mitochondria took a different evolutionary path before they were captured by cells?

There are also a few other really weird cellular-scale life forms I forget the names of that could be different evolutionary paths. Though I’d think the seeming hegemony of life comes from life competing in the same environments and either killing off or adapting to/with other evolutionary chains like with mitochondria. It surely wouldn’t take billions or even millions of years for microscopic life to spread across Earth, so there’s been plenty of time for any different upstarts to mix or kill off each other.