It is true that there is no need to doubt it because for long-term investment Ethereum is a safe choice,
so no need to worry when holding it in the long run,
until now Ethereum is still the king of altcoins.
ETH is still known as the king of alts because of its ranking in the market and despite that many other altcoins that are being said to have better networks, still remain the top choice of the many. I still also hold ETH and they're just a few of it and hoping that in the next bull run, I'll dispose of them and sell them so that I'll get a decent profit. But from there, I will not hold eth anymore as those are like the few ETHs that I'm holding ever since so it is like a make it or break it for me.
It's all about trust, though there are a lot of new protocols that might provide better options and convenience to users such as lower transaction fees, high transaction speeds, interoperability, and much more, and they also provide developers with better tools and products for creating their own projects and smart contracts, after all that, Ethereum still stands on the top and the reason for that is that people trust the cryptocurrency and don't want to leave it.
In terms of usability, there will be altcoins that will compete with it in the future, but in terms of trust and value that it has gained for itself over all these years, that is irreplaceable for any altcoin no matter how good it is, so Ethereum in my opinion will go a very long way along with Bitcoin.