Polkadot offers better scalability than the ethereum blockchain. It offers relay chain, cross-blockchain features, forkless network, decentralized governance and all these are not available in the ethereum network. Actually, Polkadot offers all the solutions to those problems that the ethereum network can not. So many projects are using the Polkadot network. Do you think Polkadot is really Ethreum killer?
Polkadot offers a lot, but only global acceptance decides success.
Meanwhile ETH continues to enjoy that ...
This is the truth, global acceptance is much important when it comes to cryptocurrency. As of now bitcoin and ethereum is the much accepted cryptocurrency in the global market. When the market keeps widening there'll be need of advancement. Maybe the same will be fulfilled by new cryptocurrencies. So we can't conclude that ethereum gets replaced by Polkadot, only the demand gives the result.