If you browse a few of the ISO pages for other states/regions you'll see a bunch that have excess capacity above their projected peak for the day.

Here's one: https://www.iso-ne.com/

Here's another: http://www.caiso.com/TodaysOutlook/Pages/default.aspx

But there's a limited capacity for Texas to bring in power over just 5 connections, combined with their choice that makes conversion to something compatible with the Texas grid much less efficient.

By isolating & not focusing on compatibility they have made it very difficult to have more robust redundancy in their grid.