It's a simple answer. Cardano can't replace eth.. definitely not possible
Very true.
Compared to modern Ethereum, Cardano is a really outdated coin and it had plenty chances to overtake Ethereum but Cardano did not achieve to overtake Ethereum.
Now, more modern coins like Avalanche will be passing Cardano itself, where we will possibly see an Altcoin overtaking Ethereum.
But Cardano has finished, it really needs a major success to get relevant against Ethereum again, where Cardano is far away currently.
Cardano is losing ground to Ethereum.
Yeah Cardano may never overtake Ethereum. Assuming Cardano continues to focus on the upcoming updates to the network we can expect Cardano's massive adoption rate but with the upcoming bull run a new altcoin season followed by Cardano making unprecedented new highs could not.