Robinson rules the trainer market
But the R22 was not designed as a trainer. The problem is this, there is no low cost purpose built trainer.
If Cran is correct in his opinion that the heavy engine is the major shortcoming of Franks R22, then the solution is a larger rotor diameter. A larger rotor would provide more lift per horsepower, a better autorotation and less twitchy cyclic. More suited to training. The only compromise would be slower cruise.
Since the R22 was not designed for training its hard to criticize the design as a trainer. But since the helo is in fact the most popular trainer it should be criticized so that any student has full knowledge of this fact. I think the R22 is a delight to fly but with my present knowledge of the accident history I have no further plan to fly any R22.
The FAA certification process is a formidable hurdle for any newcomer wanting to build a trainer. The FAA has unwittingly granted Robinson a monopoly for trainers with a design not intended for training.