While what you say is correct, the problem with your solution is cost.
In the UK, the following:
PH2.1 + LidarLiteV3 + PX4Flow = £500.
Bear in mind that you can buy a copter which can perform a stable hover, by DJI for around £1100. You can also buy a cheaper Chinese alternative (you will need to investigate this).
The other issue about that setup is that I have not seen any videos of indoor use (stable hover, shown on video, for around 5 minutes). I may run that test, but I want to exhaust the capabilities of the Erle Brain, before I look to try out the expensive set up above.
In summary, to say that you can achieve a stable hover, if you spend ridiculous amounts of money, is a given. What we need is to find the cheapest way of achieving a stable hover, indoors. My advice to anybody looking to investigate indoor stable hover, is to look at DJI drones and also some Chinese drones, then check how they are able to achieve this. I know that DJI uses multiple cameras (which is similar to the PX4Flow solution), to achieve a locked hover.
Also, when viewing videos on youtube, make sure that the video is long. There are some people who have a disastrous flight, but have 15 seconds of good footage, so they edit out the disastrous part of the video, only showing you the successful part. If you check through my videos (I have posted more videos on this forum than probably any other user), you will see that I always make sure they are long and full - no 15 second edits.
The other thing is that independent developers (on this forum) need to collaborate and share their data with others, to help speed up progress. ArduCopter is open source, with many contributors, which has ensured that the software develops at a fast pace. With this in mind, I have shared a lot of my data and findings on this forum, for others to see and learn from.