Nood question about layer 2’s

I understand that ethereum layer 2 solutions are implomenting optimistic rollups solutions and ZK rollups to compact transactions into a bundle thus making gas fees cheaper. Project such as Cartesi are attempting to make ethereum faster and cheaper. But when ethereum inevitably upgrades to proof of stake, won't these layer 2 solutions be obsolete?

Cartesi is branching out into other markets to bring developers to crypto via adding additional computing languages and operating systems to attract new developers, so they are in more than 1 market. But will projects who's main attraction is a "cheaper version of ethereum" such as solana, become obsolete?

Noob questions I know, but this is a question about projects who will fade in relevancy over the upcoming years due to ethereums upgrades. I've only really followed 1 layer 2 solution (cartesi) so I don't understand the other alternatives and what effect ethereums proof of stake will have on layer 2's