was suspecting the same.The difference is quiet simple. Rudra is just an armed version of Dhruv. You could compare its role somewhat like MiL-24 or MiL-35 sans armour. Whereas LCH is a dedicated attack helicopter. Given the war scenario, Rudra is much more vulnerable to ground attack then LCH because of its size and profile. Moreover LCH has been optimized to carry out combat is high altitude whereas Rudra is not.
Rudra is more suited for simple CT role with troop carrying capability.
also, wasn't the Dhruv's engine modified to be able to serve in high altitude areas like siachen? i figure Rudra would follow suit too