From my observations, apart from the value of tightly flown circuit work, basic IF/stick and rudder skills are honed maximally by exercises such as -
(a) initially: the old climbing and descending timed turns exercise, simultaneously from and to a heading, from and to an airspeed, and from and to an altitude
(b) subsequently: hand-flown, raw data, ILS in 0/0 conditions, progressively improving to a satisfactory landing and roll out. The simulator excels at this by sensible use of freeze and reposition. Not something that one is ever likely to do in anger .. but smartens up the scan rate and smooth handling like magic
(c) and raw data EFATO, progressively reducing to a min weight, min speed schedule at SL aft CG, with a requirement to track the opposite end localiser. Again, freeze and reposition permits maximum repetitive practice. The pilot who gets it all under control with a failure during the rotation flare usually goes off home at the end of the program with quite a (well deserved) swelled head ...
I have used the above three exercises, sprinkled throughout initial jet endorsements with both high and low time pilots .. in the great majority of cases, progress is fairly rapid and pleasing to watch from the back seat. The spin off to the other standard endorsement flying exercises is patently obvious to the back seater.
The automatics don't get a look in for this stuff ...
Clearly, the back seater has to be of a suitable personality to keep extraneous stress levels low in the front seat so that full concentration is on the exercise and no worry about the learning curve screw ups along the way and what the back seater might think of the pilot .. indeed, this back seater had little but high admiration for the hard work put in by the typical endorsement student.
... the end goal justifies the means ...