The only reason I see it would be
smart to do PPL in a MEP if the student owned the aircraft and it would be cheaper to fly his own twin than rent a single-engine trainer - if such aircraft even exists, which I highly doubt
As previous posts explain, losing an engine in a light twin doesn't mean you lost 50% of all your power - ~ 90% is much more realistic number. I suggest reading
this article - especially look at the numbers. Flying is all about risk management, whatever the aircraft type/size/number of engines - and engine failures really aren't that common if you compare it to number of CFIT accidents.
And as IO540 states, it's nothing complex about handling a VP prop and retractable gear - it's usually the speed of the aircraft, which is why you must think much more ahead than with an usual spam-can.