The 40X multiplier goblin's possess exclusively applies to walls.
In a world where CC troops can be lured out and attacked by flying units, the goblin finds itself in a disadvantageous position. The fact is they are the fastest unit, and while this may come in handy sometimes, it usually backfires when the troops are easily and hastily lured out and dispatched by an smart adversary. In addition, being unable to attack airborn units makes their protection duties limited, while it also makes them useless agains all-air attacks.
Stick to ranged units for defensive purposes. That being said, no troop is bad for attacking. And the goblin finds its niche for coming out en masse.

