I think I can see how the Gorilla gate might help against Tow Cables. It might be able to fold its legs in such a way that if it suspects tow cable attacks, it can drop to the ground without exposing the underside, which doesn’t seem like an option with the AT-AT walker. Likewise, they talked about possibly cutting the cables with the bulk, but it seems the front legs also seem to have some sort of grill, which might indicate they are either blades or hide blades to just saw the cables apart with.

As for “bigger is better,” remember that the First Order is supposed to be loosely based on Nazism, and a big thing about WWII Germany was a desire to create larger and larger weapons.

Edit: Oh, and the gun on the back: If its gate allows it to drop the way I suspect it to, then the gun on the back instead of the head means that it’s still be able to pose a threat, unlike an AT-AT, keeping your angle of attacks even further limited (as now you have to try to hit the neck from behind rather than head on like in Empire.