Who cares if they have done all their training in a DA42 or say a seminole. What about those that only train in G1000 aircraft from day one? Really the DA42 is a great training aircraft unlike the seminole and early seneca's you can still climb with one engine inop.
What about those guys who fly for the airlines that flew the old school DC3s, 707, DC8s, etc. To those that are jumping into a CRJ and all the full automation jets. Can it be a step back if a student wants to fly a traditional multi aircraft, yes, but thats what a checkout is for with a MEI.