So your explanation comes down to:

The AI is smart to stand there and be slaughtered without a single enemy kill because if it did something else, it might lose? And you don't see a problem with that "logic"?

Defending the square is only useful if you, as the human, don't bring any missile units. A very simple "If you are in the square, and being pelted by missiles, attempt to engage the missile unit" would be effective. Even if it was HA, and they couldn't catch them, they couldn't have a worse response than doing nothing.

Bh