There is certainly and argument that training to operate a 2 pilot jet is quite different from a single pilot piston. So much so that an extra course - the MCC - was introduced to help bridge the gap. Clearly there are single pilot traits that do not transpose well, and anecdotal evidence to suggest that too much single pilot time could make someone harder to train multi pilot. The MPL is designed with MP operations in mind from the get-go, and the stick and rudder argument is less of an issue when the other guy has 3-4,000 hours. Yes, a brand new MPL could find themselves single pilot thanks to a dodgy fish course, but that would almost always result in a diversion to the nearest airport with vectors and probably an automatic landing - arguably one of the simpler emergencies. It could also happen to a brand new CPL (with half the SIM experience).