These are the most 2 common way of working in game design, there’s the top bottom process or the bottom up process. This is where Bottom up process and Atomic design can make a difference to your game. I’m pretty sure that the equivalent enemy can be found nearly to the end of the game in Gears of war.
Gears of war first encounter challenge minimum player skills while Avatar first encounter is challenging the player with all his parameter set at the most difficult rate. Gears of war have been built with having the player skill’s challenge in mind while Avatar doesn’t. The player must only hit one bullet on the bomb to make it explode. In Gears of War 2, the first encounter (The bomb) is a good size on the screen, don’t move, is always visible to the player and there’s only one that is taking eliminating a bunch of enemies at the same time. The player must hit multiple bullets on each target and there’s multiple of them. In the Avatar game, the first encounter (The dogs) is a small enemy, that moves really fast, that is often not visible to the player and there’s a lot of them.