can you say more to convince me that ETH's moat is based on some kind of network effect?

There is definitely momentum to capital being drawn to other capital. Having capital in a protocol for a long time without hacks is it's own type of proof of security. So when more capital wants to deploy, it chooses the protocol with the best security record. Users may care about a $0.05 transaction fee, but hundreds of billions of dollars of bank deposits coming to the chain or a tokenized securities marketplace won't care about that nearly as much as security. There's also the fact that Ethereum has never once had downtime since inception which can't be said of Solana or Ripple even in the last year.

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I frankly think the market undervalues decentralization to the extent they even understand it at all. I agree with you that the security only needs to match the level of the transaction; that's basically the point of Ethereum's L2 model. It's worth noting that Solana isn't practically much cheaper than most Ethereum L2s at this point. The TPS numbers of Solana are deliberately misleading in that they include validator gossip where Ethereum's TPS numbers do not. Ethereum will outscale Solana for fundamental reasons. Maybe read Polynya's blog if you're curious. He was posting in like 2021 about fundamental truths that Solana will never be able to address with their approach.