One small problem with just teaching everything once is that complex manoeuvres like autos, quickstops etc need to be repeated on a regular basis if a student is to achieve any level of competence and finesse.
If you do it all on a twin and then send them to an OCU it will just increase the burden on the OCU because you have removed basic and advanced training and just given them basic training on a twin instead of a single.
Exercises that were a revision on the twin after learning them on a single will either have to be practised more on the twin (more hours and cost) or you will have to accept a lower standard of output to the OCU (hardly ideal).
Part task trainers and simulators have their place but they will never replace flying the aircraft as a way to build skills and confidence - not to mention airmanship. Even the best sims can still be flown as a playstation game (don't touch anything and it stays where it is) which is great for the playstation generation as far as passing sim rides goes but is coc*-all use for training pilots to handle the real aircraft.
We might all like to think that when we were students, we only needed to be shown things once and we were the ace of the base - if that was so why do we teach fault analysis to instructors?
I think the mirror Sqns at Sy is a good idea - the whole 660 705 concept of ops was, as mentioned earlier, a sop to Service pride and a hindrance to effective flying training.