Personally I think the biggest issue with crypto now is, one that it promotes huge value inflation and Ponzi-like schemes (we are seeing it with BTC and ETH), two horrible energy use inefficiency. From a bitcoin transaction that requires orders of magnitude more energy to process than any other transfer of value known to humanity to Ethereum "virtual machine" for smart contracts that is most inefficient way to execute arbitrary code ever invented...
I used to be a big proponent of crypto overall. I still have some holdings in it, but I can't unsee the idiocy in PoW crypto once I saw and understood it clearly.
I wondered for a while what is so specific to crypto that it became today's tulips? (Rather than gold futures, stocks, real estate etc) and then I understood all those asset classes are already used like this. Every kind of asset that can will eventually be used in some kind of pyramid scheme. Just look at the price of gold compared to few years ago, real estate in many large cities, stocks etc. It was absolutely inevitable that crypto as it became a trusted store of value would become a vehicle for speculative bubbles/pyramid schemes.
So then the question is, can crypto fulfill the role of a currency (requiring some level of value stability) and be a vehicle for speculative pyramids at the same time? I don't think so.
Proof of Work is one problem with crypto that perhaps Proof of Stake will resolve.
The other problem is much more fundamental. How do we create crypto that maintains stability without having to resort to typical "stable coin" strategies like holding other currencies and selling/buying them to artificially adjust the value. Is it possible to create crypto that would maintain its value in the long term in distributed - no central authority manner while discouraging pyramid investment schemes.
And finally, once someone invents such crypto would anyone actually hear about it as most promotion of crypto seems to be done by people who got in early and hope for their holdings to increase in value.