Cardano cannot replace ethereum because ethereum is very successful after Bitcoin and as Bitcoin cannot be beaten by any coins the same is the ethereum which is not possible to be beaten by any other altcoins. Cardano is successful and profitable but we should not compare one coin with another because every coin has its own level of success and has its own value.

We don't Know what will be the coming years but currently both cardano and Ethereum are profitable but here we cannot say that Ethereum will be replaced by cardano or cardano will be more profitable than Ethereum. The value of cardano will increase but Ethereum will also increase in its price instead of keeping a single worth forever.