Give me the Bonecrusher lore I deserve
So, to fully understand the Bone Crushers you need to understand the standard operating procedures for the Empire’s territory acquisition.
On Mars the largest Legion is the Sand Eaters. The Dust Giants are, according to destinypedia, a subdivision of this legion. To that I say no, they were a subdivision. Since their founding the Dust Giants have become their own Legion.
Amongst the Dust Giants is a subdivision called the Siege Dancers. These yellow and blue beauties are basically storm troopers whose job is to secure new territory and erect fortifications.
So on Mars the Cabal’s procedure is pretty straight forward. Sand Eaters defend the area calling in for Dust Giants when they need back up. When lines have been lost or an opportunity arises, the Seige Dancers will go forward and reclaim lost or new ground. Though in the time period between the Taken King and the Red Legion arriving, I can see this happening less with the Cabal’s reduced numbers, with the Seige Dancers helping hold positions rather than fortify new ones.
The tl;dr is that basically the Cabal have an assault group that goes and gets ground and fortifies, and a defensive group who holds these positions.
However, not all combat is in open spaces like Mars, and this is where the Bone Crushers come in.
The Bone Crushers are a specially trained Legion for fighting in urban and heavily built areas. They would rely less on vehicles like interceptors and tanks because of how much of a target the can be for ambushes. For example, if a column of tanks is advancing up a road in a city and the leading one is destroyed, that kinda clogs up the road a bit. And this is assuming the roads are big enough for these vehicles. Instead they often work on foot and use vehicles like the one on the right (please ask me about them because I won’t go into details here to save time).
But yes, the Bone Crushers are specialised Legion for fighting and securing built up areas. I will give you more when it comes.