I mean, if someone says that (a) proof of work is the only viable solution and all others have flaws you can't get around, (which I have noticed people claiming) and (b) BTC is still the most successful cryptocurrency, which people are not abandoning, what's your response?
You just made a string of assertions without explanation, so why do you think these things?
Well (a) is simply wrong. Proof of works has flaws (energy wasting/tends to centralize) which can not be fixed. But others have fixed these flaws by not using PoW.
Yes there are people telling that PoW and Bitcoin is the best and all other systems are flawed. They are called Bitcoin Maxis, their arguments usefully fall flat when you apply logic. They don't even agree with each other about which Bitcoin is the real Bitcoin.
>BTC is still the most successful cryptocurrency
How do you measure success of a cryptocurrency? Also being the first gives huge advantage for "success". Like Whatsapp which is probably the most successful instant messenger but does that mean it's the best? It takes time to dethrone something like Whatsapp or Bitcoin just having the better tech isn't enough to instantly make everyone switch.
>You just made a string of assertions without explanation, so why do you think these things?
You have any specific question? I don't really know what I should explain. If you are interested in alternatives to PoW you should lookup XRPL Consensus (Federated Byzantine agreement) a variant of this is also uses by the Stellar Consensus Protocol. Then there is PoS which is the most known alternative. DPoS is building on top of that idea. Then there is PoWeight, Tangle, Hashgraph and some other less popular and/or not (yet) working ideas/theories.
You just made a string of assertions without explanation, so why do you think these things?