So Trashman, in no particular order.
1) If you're going to have the AI run away into the UFO, then you may as well start the game at the UFO, sans artillery. What's the point in walking across an empty battlefield, People get bored when nothing is happening.
2) If I don't always have the option of having artillery because reasons, I'm going to prepare as if I never have it. If I prepare as if I never have it, then why do I need it in the first place? So that the AI can run to the UFO? Anyway, people are going to point to the aircraft that Xenonauts have, and ask why they can't use those instead of unreliable artillery.
In any case, you acknoweldge that artillery is unfair. Unfair when I have it, unfair when the enemy has it. It's an I win button when you apply it to a skirmish-level tactical game. It's why PP at least put the artillery on-map so the other side has half a chance of stopping it.