I don't think Cardano will replace Ethereum. and I don't see any reason for that to happen. if you are saying that on the basis of transaction fee then Cardano can be used as an alternative source to send and receive payments, but replacing is really different which I don't think will happen.
Cardano is the winner in term of Transaction fee tho.

Both blockchains can be used for pretty much everything. there are tons of dapps, defi protocols, gaming and nft projectts built on top of Cardano and Eth blockchain.. but are equally competing with each other in these aspects.