I think it's definitely different from insta-kill.
With insta-kill, you don't even have to move, don't have to be in strike range, don't have to deal with potential terrain impediments, don't have to deal with potential troop weaknesses or any of that. You remove four units from the enemy irrespective of their defense.
However, with the second method, you gain the advantage of extra movements, but still have to contend with all those things mentioned above. It's true that for those players with massive attack boosts that it may provide the edge to crack a previously uncrackable defense, but escalation is part of the game and the defender will just have to get more defense if they want to remain impenetrable. Being impenetrable is a great achievement, but it isn't a right.
* As a side note, now I know why Iran want's nuclear weapons, lol.