Exactly. Cardano may be a good cryptocurrency with a huge vision to transform the blockchain industry, but so far, its development team has been slow in contrast to other platforms like Ethereum and EOS. This way, Cardano may never destroy or replace Ethereum, since Ethereum will always be in the lead of development and innovation. However, one thing that ADA could do is to complement Ethereum as an alternative smart contract platform for the mainstream world. ADA could use just Ethereum's help to improve itself over time. The same thing could happen vice versa with Ethereum.
Based on facts, Cardano's co-founder (Charles Hoskinson) has worked on Ethereum before. This means, that he has some experience related to how smart contracts work unlike any other. Perhaps, Cardano would succeed over time, as Hoskinson guides it every step of the way. On the other hand, Ethereum has Vitalik which is also experienced in the field of smart contracts and blockchain technology. Both platforms have good leaders that have a great vision towards making smart contracts practical for the world.
Nonetheless, time will tell us whenever Cardano will remain alive and actively supported by people in the mainstream world or not. Just my opinion