This, it's that simple.
I honestly said do not get why you're bothered by something like this.
Options 3, 4 and 5 aren't even viable ones; 3 and 4 are plainly impossible and 5 doesn't even provide any input.
Option 1 then isn't even particularly relevant. The correct questions are first what amount of strength is needed to destroy Noah? And second how would, using that strength, Noah be destroyed the fastest? Whether Gear 3rd is stronger than Gear 4th or vice versa doesn't matter if both of them have enough strength to do it. So you automatically end up with option 2. Gear 3rd was simply the most suited for the situation. Even if Gear 4th has more power, its impact is far more focused on a single point. Gear 3rd has a far larger range of attack. The area one attack of Gear 3rd covers is like a 100 times that of Gear 4th.
Compare it to a sniper and a canon. If a sniper shoots through the head, it's a one-hit kill. Accurate, focused, efficient. That is what Gear 4th is. If you want to cause wide-scale massive damage however, then a canon is far more suited. There will nothing left of the body if hit by a canon nor of the area where the person stood. Even if you would hit the body with a hundred sniper bullets, it still would not get the same devastating result as with the canon. So when a huge-ass ship is falling from the sky, you want to use the canon.
It's that simple.
