Im a bit confused on what your saying about swapping stuff lol
The idea with the Mangler was to use it as huge distraction and force the opponents hand to deal with it immediately but i could probably drop it in favor of more spread out bodies. Smaller looking threats wont look as nasty so might catch people off guard.
The Rockguts are there for cracking big guys, ranged MW, and being tanky heavy infantry. A good back up I would say slogging behind or between the Herds