I came to an odd conclusion, watching ROTF... Devestator is not a combination of the other Constructicons, he merely is A Constructicon. He transforms into a fleet of construction vehicles, then back into one robot mode. All are connected to the one conscience. Basically the same idea initially proposed for Arcee, but ultimately ditched in favor of the triplets. In the movie, there is no hint that Arcee, Chromia, and Purplebike share any bond outside of sisterhood. When sisters get shot, there is no reaction other than horror. The other constructicons we see as robots (LongHaul, Mixmaster, etc) are not connected in anyway to Devestator. That also explains why when Devestator takes the railgun to the gut, he falls apart into chunks that do not convert to individual robot modes. Does this make sense?