> Why does Bitcoin need to modernize?
Because ASIC vulnerability has led to the concentration of the majority of the world's mining power among a small number of organizations in China, and because the amount of power consumed securing the blockchain with PoW is silly and ever-increasing.
> There are other crypto projects that can fill in the holes that Bitcoin leaves (tx fees, slow, etc).
It's not just about filling holes, other cryptocurrency projects are superior technologically in every way. And since Bitcoin has been demonstrated to be impossible to modernize this gap will only become more extreme over time.
Bitcoin remains the locus of the cryptocurrency movement through network effects alone, which is why evangelists are so adamantly in favor of Bitcoin specifically. If it loses its throne as the "main" cryptocurrency it will never increase in price to the value that Bitcoin speculators are hoping because other than its network size it has no advantages.
> It needs to WORK, and work very well, which it has demonstrated.
I think it has categorically demonstrated that it does not work, at least not for the purpose that the original Bitcoin paper laid out. The fact that Bitcoin transactions are slow and expensive has so compellingly demonstrated that Bitcoin cannot be a useful cryptocurrency that even Bitcoin advocates admit this and have fallen back to claiming that it will instead be a store of value and that an effective currency layer could be built on top of it.