Having lived in Texas during Beto's fight against Cruz, I'm pessimistic.

The redness is baked in. Republicans have begun to win over the Tejano vote along the Rio Grande, as you mentioned. Beto needs to get that vote back to have a chance. He can, I think. He's very popular in El Paso, and speaks very fluent Spanish.

Unfortunately, the type of recent arrivals from California tend to lean libertarian, which is one reason they are leaving California. See Musk, Elon for an example, but I can also say from personal experience/observations that the type of Californians Texas lures are not exactly AOC fans.

Your conclusion is still legit. The governorship IS within reach. But it'll take a small miracle.