Actually I found the UK initial multi-engine IR training to be the hardest thing I've ever done.. It was certainly a damn sight harder than the subsequent turboprop, A320, A330 or command upgrade training. ATPL subjects and single engine VFR stuff weren't that bad. Maybe a personal thing but for me, that IR was the peak of the difficulty curve and the closest I've ever come to giving it all away.
Apart from that you're right seventhheaven, in my 5 years and couple thousand hours instructing I can think of honestly 2 people total who I thought just didn't have the situational awareness / motor skills to get there. The rest of them it was just all about the confidence and the pace of learning, they all got there in the end
