Does it actually need to render to play? You can turn off background rendering in preferences and render out later, In my experience with the software it seems to play almost everything without rendering.
Black placeholders are gap clips, just like in Avid as for everything else, that’s the way the software works, it’s different, you need to learn exactly how it works to avoid some of the issues you have mentioned. There are lots of resources out there that will tell you how to work correctly with FCPX. I would highly recommend them if you continue working with the software.
Otherwise PPro is a great alternative
“My Name is Steve and I’m an FCPX user”