There is no scientific literature correlating added weight to fewer injuries, but I’m pretty sure you can find epidemiological studies that show a correlation between increased weight and a greater risk of overall injuries in not only the general population, but in a subset of those that are in athletics.
Greater weight puts a greater strain on every joint and ligament in the body. That’s a physical fact that’s indisputable. Clearly, if in the process of adding a sensible and moderate amount of weight you increase muscle strength around the joints and mind to increase ligament and tendon flexibility and strength through stretching and other exercises, you should be better off.
The clear objective is not the absolute increase in mass that weight gain affords, although I’m sure the staff wants some mass increase, but more the increase in strength. Especially with someone like N’Kosi, I would be more concerned with him increasing lower body strength, that would give him better leverage and ability to evade the rush, improve balance, and get away from the grasp of possible tacklers, than just “increasing his weight”
The focus on increasing weight is misguided. It’s about increasing strength.