The MR wash into the TR has nothing to do with TR Vortex Ring State, they occur at vastly different conditions.
The MR wash into the TR does cost about 5% of TR thrust, which is a blip on the HQ diagram for a helo with a right-sized TR and a disaster for a helo with a marginal TR. The issue is not the mystery of what happens, and "If I cant explain it, I can't control it." The issue is how the designer builds enough moxie in the design to handle the predictable effects that the real world provides. Like jack stall, LTE is predictable and preventable.
Evidence the fact that the OH-58D had LTE when the US Army first tested it, and they walked away from the aircraft. A few weeks later, a bigger TR was fitted, and the OH-58D has not had an LTE event since.
Mysteries like this are like picking your ears with a hammer and nail, if you are confounded by the blood, maybe the fault is not random circumstance.
For the record, IMHO the B-206 is a classic helo, and rightfully goes down in history as a great one. Like the S-61 however, just because it was great does not mean the waterline for safety is permanently set at the level that we have had to live with. If we mistakenly agree that the weaknesses of yesterday's helos is all that we ever need in future helos, we condemn all future pilots and passengers to suffer that way our fathers did. And for that we should be roasted slowly in hell.