I think his analysis is flawed. The only serious argument is not that the verb “established” is undefined. It’s that the language relating to tax credits specifically allows them only when an exchange is established by the State, and the statute further specifically defines “State” as “any one of the fifty United States and the District of Columbia.” (Another point that no one in the thread bothered to mention, despite plaintive cries that “State” could mean the federal government.)
He ultimately says that the courts should look to the overall purpose and forget the words.
But the words show the purpose. Congress intended to incentivize the state exchanges. They expected that states would all have exchanges. That didn’t happen. The courts should not re-write the statute to fix a mistake of that nature.