You are right, it’s up to MTH to control the quality of a product that they have others build for them, China or USA.
I have not had any problems with packing from Lionel, MTH and LGB (LGB seems best). Aristo-Craft has. Loose wires and plugs is a design problem.
You can not “scale” up a 2 pound locomotive to a 20 pound “G” gauge unit and use the same packing system. Nor should inadequate body and frame construction be used for a heaver locomotive. PC Boards should not be effected by shipping impact.