You think all of that can be blamed on HF20? That's a bit much, IMO. Yes, the resource credit system had issues that needed time to work through. I had conversations with people to help explain what was going on at the time (such as "Steem Is Broken!?!" A Conversation with Sida of Partiko) and most people figured it out.
What really drove people away was the cryptomarkets tanking into a bear market that lasted for years. People were here for the rewards and the cryptocurrency hype in the news cycle. When that went away, so did the people who were here only for the rewards. See my post which goes into more detail on figuring out why you are here if you want to stay long term.
RE: HF21: What Makes Steem Valuable?