It's not a failure because Bitcoin tanked (relatively), it's a failure because Bitcoin tanking was and will always be a significant risk. People who got rich from Bitcoin weren't savvy, they won the lottery. It's not a sound investment decision based on outcome. Investments are sound based on probability and risk beforehand.
El Salvador gambled which is stupid. Whether they won or lost at the lottery is inconsequential to its stupidity.
It is a failure because BTC has pivoted away from the Bitcoin whitepaper (p2p ecash), limited its blocksize and has taken the path of this strange "digital store of value" (lol). BTC's activity rose gradually up to 2017, and then topped off at 1MB and even dropped. [1]
If Bitcoin's momentum hadn't been dissolved, it wouldn't require people to be forced by State to accept it.
[1] https://bitinfocharts.com/comparison/size-btc-ema14.html#all...
Growth continued on second layers: Bitcoin's tx count on the Lightning Network has doubled over the last year. Forks of Bitcoin who attempted to scale by increasing the blocksize all failed and are practically dead (Bitcoin SV, Bitcoin Gold, Bitcoin Cash, eCash, Bitcoin ABC, ...).
Someone needs to explain to me how the Lightning Network actually works, because I find it super sus. How do people make money off transactions as miners if BTC transactions are so cheap ?