NDAQ market cap: 15 billion.
Value of stocks listed on Nasdaq: 9 trillion.

It is an extremely bad assumption that value of ETH will be greater than the value of ERC20 tokens in the long term. There is no reason for ETH to add the value of AAPL if Apple decided to issue it’s stock on Ethereum. I definitely see a few ERC20 tokens exceeding the market cap of ETH, for example DAI.

With multi-collateral Dai there is absolutely no reason the value of MKR should be tied to the value of ETH, one could have more market cap than the other. Especially if Dai branches out and is issued by on other blockchains too. MKR will be valued based on total DAI issuance and ETH will be valued based on it’s network usage.