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?
maybe for now polkadot is the best ethereum competitors
but i never think if polkadot will replacing ethereum as the best altcoins, remember ethereum community is very strong buddy