because we are supposed to be pilots and, if the AP fails IMC who is best placed to make a safe recovery - the pilot who has practised AP out or the systems manager who hasn't
You miss the point. Setting aside the fact that if you ever get to fly a modern helicopter you will come to know that the levels of redundancy are such that AP failure is almost inconceivable, there is only any point in training for a scenario that could actually occur. As I said, on the 225 at least, it's not feasible to have a failure where HDG doesn't work but the AP works normally in ATT mode (ie the mode it's in normally, without any other "upper modes being engaged). So why conduct lots of training in ATT mode? A complete waste of time.
Certainly, train for realistic failures such as SAS mode and complete autopilot out, but let's target training on what could realistically happen, not just on something "because we've always done it that way", ie mindlessly.
As an aside, the primary and as far as I know only ever occurring reason for loss of AP functionality on the 225 is the pilot pressing the AP disengage button accidentally. I've certainly done it! So as well as training for that specific event (requires PM to swiftly re-engage the AP) why not put a bit of effort into making that event less likely to happen.
Helicopters crash for various reasons, often on a repeating theme, but these are not single engine failure nor an inability to fly with the normal AP engaged but without use of the upper modes. So why do we continue to expend so much training time on these things and so little on the things that repeatedly cause crashery?