Yeah well during that disaster Oklahoma and Mexico were having the same problems and didn’t have power to spare. ERCOT is not an Island, it is a huge entity with connectors you shills.
During the disaster the new head of the EPA forced Texas to set the price at an astronomical rate in order to run the coal and other plants at 100 percent. The EPA caused Texas huge financial pain that we are still paying for that $9,000 / MWh event.
On the national grid it is. They are separate. There was talk of an AC/DC to DC/AC substation in Oklahoma (Because they are synchronized with each other) to allow transfer of power but I don't know if it ever got built.