I would say 85% + are probably mixed… maybe. For most of the last forty years mine have usually been. Components tend to differ, so the solution for any two components will likely differ. Sometimes I acquired things at different times and I found a better match.
For the first time I have nearly all the same power cords, cables and interconnects.. but still, I needed to switch brands on my power amp. But now also all my electronics are the same brand and level… something new to me. You can see my systems under my user ID.