Unless I've totally misunderstood, I don't think you're right.

For instance, on your first go, drop in column 0. Then, the AI drops in columns 1, 2, 3, 4, leading to this:

    . . . . . . .
    . . . . . . .
    . . . . . . .
    . . . . . . .
    . X X X . . .
    X O O O O . .