For any good new coins in the cryptocurrency market there will be enough space and no one will destroy anyone. A coin can leave the market only when a certain time does not bargain. This ethereum is not threatened yet. Moreover, in ethereum, significant improvements are expected not only on February 27, but also at the end of the year or at the beginning of the next. Therefore, I think that ethereum will always be in demand in the foreseeable future.
Exactly. Ethereum will always be on top of other cryptocurrencies because of its first-mover advantage just like Bitcoin. Cardano may have greater technologies, but it's not as popular as Ethereum. Not to mention, most dApp developers are building on the Ethereum blockchain than most well-known smart contract platforms today. Which is why, even if Cardano grows in development and innovation, Ethereum will always be in the lead.
Given the diversity of cryptocurrencies with unique features across the whole market, it's very unlikely that Cardano will destroy Ethereum (or vice versa). The future lies in cryptocurrencies which provide the lowest fees possible, fast speeds, and most of all, resilience. Which is why, Ethereum, Cardano, and other leading cryptocurrencies will remain in the market for a long time. They will continue to improve over time, until they become a mature blockchain platform for the whole world to enjoy.
Nonetheless, it's good to have this diversity in features and technologies, as it will benefit Blockchain technology for years to come. Cardano is a good cryptocurrency, as well as, Ethereum. Investing into them now, would be the smartest decision to make. Still, do your own research to find out which coin is the most suitable for a long-term investment. Just my opinion