Sounds like you just bought lemon devices with the issues having nothing to do with Android itself. I have an LG V40 and it works just fine with none of the issues you mention. I previously had an LG Optimus G and it also worked fine (it's slow by modern standards now, but was on par with devices at time of release). My family also had a Moto X, which can still run but was replaced by a Moto G7 when 3G service was shut off. The Moto G7 is also very snappy for a dirt cheap entry level phone.
I also have two cheap lowest end Samsung tablets. A old Tab A 8.0 that I used for navigation in my old car and it worked fine for that purpose. It was not snappy, but about par for what you would expect for a cheap device at the time. Didn't have issues with crashes. Also got a Tab A8 in the recent few years and it's considerably snappier, and also no issues. What kind of Samsung tablet did you get?
As for Chromecast, that's entirely unrelated to Android as it runs its own OS. I personally use Amazon Fire TV devices which actually run Android and they have worked flawlessly. Even my oldest one runs very snappily, much better than the Roku device that was bundled with an internet provider. I opted not to get Chromecast because Android is far more flexible (I was able to sideload apps like Kodi onto my Fire TV devices).
