I too would be very angered by a drunkard waltzing through my door, yet if I commanded the boozer to leave and he did...it's shaping-up to be a decent night without a gunfight.
The point that we seem to be missing here is that the victim was described as elderly while the criminal was described as being in his early-thirties. The homeowner had complete superiority by being in a fortified position (his house) with access to firearms, telephones, lights, and anything else he might have needed.
The imminent threat was over and the older man put his wife in a weak tactical position by abandoning her and going outside.
~ Blue Jays ~
He left the house but not the property. That's still a threatening position - could be waiting for friends to come and reinforce him.
You do know that rural houses in TX have their utility connections exposed on the outside of the structure, right? It's stupidly easy to cut telephone lines, power, and remove some of the other "advantages" the homeowner has according to you. In the dark of a moonless Texas night, without power, without lights, without commo, and with an unknown number of assailants, you're fair game.
He's not required by law to assess the stage of the threat. Also, he does not know the true extent of his threat. Are there more intruders? By the way, how do you know that his wife's not a better shot than he is? This is Texas. LOL
A fortified position is no match for a mobile agressor. The Maginot line was useless. A house with breakable windows, exposed utilities, and burstable doors is not as secure as the French surrender line was.