Turns out, it's quite easy to implement a decent fighting logic...
Here is an excerpt from the article "The Making Of: IK+"
The development of IK+’s AI was, though prosaic by comparison, no less efficient. “It was easy, basically,” Maclean boasts. “In those days, it wasn’t even called AI – we would have called it ‘fighting logic’, or something. The whole thing was based on look-up tables of what moves to use based on how far away the opponent was. The game obviously knows which move, if it were used, would lead to a direct hit at that point in time. For the easy difficulty level, right at the start, the computer fighters would, 90 per cent of the time, look at what the best move would be and then ignore it. As the level of difficulty increased that percentage would drop, until level 25 or thereabouts where it would be 95 per cent accurate. It worked beautifully.”