What will happen to Ethereum scaling solutions?

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self.ethereum1m ago
Apologies for the noob question (I'm a noob) and if this question has been asked before. What will happen to Ethereum scaling solutions, specifically Optimism when Ethereum migrates to POS? I'm still grabbling with understanding the Optimism project. It seems that the only thing it has going for it is that it uses optimistic roll up to solve the slow transaction speed of Ethereum. Assuming the POS eth would solve this problem, what is the role of optimism and other scaling solutions after that happens?