I'm no engineer so can't improve upon the valid comments made by WNR.
I hope I'm not being unfair, but I can't help wondering whether Lu started his research with an open mind, forming a conclusion based upon the facts which he found - or started with his conclusion, and then selected facts to support it. It does make a difference.
Doesn't the accident rate merely reflect that the R22 is the most popular training helicopter worldwide, and is usually flown by PPLs (like myself) rather than professionals?
The R22 isn't easy to fly well, but isn't that a desirable feature in a trainer?
The R44? Although I now prefer flying the JetRanger and the Gazelle, the later R44s (particularly the hydraulic new version) are a pleasure to fly.
Note:
Having suggested that Lu might have some prejudices, it's only fair that I should declare mine: Well done Frank Robinson for opening up the helicopter world to so many of us!