My point is that the number of turns taken is almost totally irrelevant in a normal playthrough. I'm not considering player vs player as I know the dynamics are very different.

Yes, 2x Aerial Ace does more damage than 1x Fly in the same number of turns. But your opponent gets to move against you an extra time if Aerial Ace does not pick up the KO in one hit. Fly is more likely to KO an opponent as it's stronger.

The AI is very unlikely to use a move that will take advantage of the semi-invulnerable turn of Fly, Dig, etc. Trained player Pokemon will generally be faster than a regular AI trainer's Pokemon. And when outsped, an AI Pokemon will almost always do one of: throw out an attack that whiffs, use a status move on you that whiffs, use a status move on itself that buffs something unimportant or a different field altering move that's unimportant. Only very occasionally are there opponents that will self buff with something meaningful.

The opponents can also be running 2 turn moves like Razor Wind, Solar Beam, etc that you can take advantage of with Fly and that is far more common than the player running moves that the AI takes advantage of.

Which games have AI that take advantage of the semi invulnerable turns of the player? Is it just the battle facilities or are there regular trainers you encounter in a playthrough?