Graders usually aren't getting shot at. The chain is very vulnerable.
The major issue with chains is that they are very high maintenance items. Dust/dirt/water are not nearly the issue they used to be now that we have synthetic grease and oil but back in those days such luxuries weren't available. The biggest issue from a break down at the wrong time I see there is that the chains/sprockets are to small for the task being required of them. On the other hand if one chain/wheel is taken out the rest just keep on working. The wear rate would be atrocious on the driven gear tooth surfaces. That vehicle would need a parts truck following it into battle. Nothing really wrong with the prime moving system other than it is to light for its intended purpose. Very likely it does operate as a skid steer. Mind you, it is a prototype.
Chains/sprockets are tough. They are also positive and without slip. My grandfather used to have an old highway truck on his property dating from pre WWI. That truck had chain driven rear wheels. He used that truck like a tractor for several farm jobs. His big issue with the truck was that the wheels on it were to small and it would get stuck in deep mud and snow. He made sure he lubed the chain frequently when in use. Chain is very expensive and in the case of that truck very hard to come by. Same for the sprockets.
I have personally maintained chain that was being used under very extreme conditions. Silica dust, water, muck, high heat etc. It always did the job until it wore out or the sprockets in the system wore out.
Most of the motorcycles I see are chain driven. That is a pretty proven system and it delivers most of the available horsepower to the driven wheel.
Chains are also small targets but as mentioned very vulnerable if they are hit.
There are other systems that are better suited to the task.
One other thing to keep in mind, the tracks on tracked vehicles are nothing more than big chains.
