Blockchain consensus mechanisms come with a trilemma whereby you only get to pick two out of decentralization, security and scalability. Different consensus mechanisms emphasize the three in different ways. Bitcoin and Ethereum both use Proof-of-Work, which sacrifices scalability for decentralization and security. PoW is not just some primitive consensus mechanism which can and will inevitably be replaced by Proof-of-Stake or some variant of it such as DPoS. I believe using PoW is the very reason Bitcoin can be as massively valuable as it is. Also, it helps Ethereum attract applications involving high-value contracts that it is very decentralized and uses PoW.

I think Ethereum is best suited for high-value contracts that require a high-level of security simply because any less security would create incentives for an attack against the consensus mechanism. But as you write, Ethereum can be used as a source of deep liquidity for projects mainly using other, higher-throughput chains through cross-chain bridges.