Cardano's proof of stake model has stronger assumptions than proof-of-work (if it wouldn't be the case, and the authors could prove it, they could work on improving Bitcoin itself...but I think they preferred to make money).
New altcoins just don't solve the problem of increasing the security of Bitcoin. Schnorr signatures are are great example of not making the cryptographic assumptions stronger (actually making them weaker) while improving the scalability of the system.
New altcoins just don't solve the problem of increasing the security of Bitcoin. Schnorr signatures are are great example of not making the cryptographic assumptions stronger (actually making them weaker) while improving the scalability of the system.