Two points that you can not grasp. The MI-24/35 is the most heavily armored helicopter in the word, it can, for instance, withstand 12.7mm rounds to its rotor bladed. In fact, the entire helicopter is protected to withstand 12.7mm rounds. Even with direst hits by stinger type rounds to surface missiles, MI-24's were able to land, most other attack helicopters can not even take hits from 7.62.
So your logic that it is easy to down is simply based on ignorance. Also elaborate on what you mean by "bulky" if you think that a helicopter like a cobra is less vulnerable to surface to air missiles then you are very mistaken, the Cobra's smaller profile will not protect it, once a missile is locked it's locked. And contrary to popular myth helicopters can not outturn a missile, so a smaller helicopter has no advantages here.
Yet Russians have been innovative in weapons design so much so that many of the designs/concepts that have come from the Soviet Union/Russia have been copied.