Hypothesis: Aeros came out 20 years ago and sold mainly to existing Morgan owners who were less familiar with complex driver assistance systems (because cars of the time didn't have so much of them). Plus Sixes are selling to new entry owners who are coming from other modern cars which are loaded with driver assistance?
Also, maybe the comparatively high cost of Plus Sixes mean that the only people who can afford them tend to be older and forget that reactions times decline quite sharply with age, making it much harder to catch a breakaway when it happens?
In this case the driver could have been a highly experienced Morgan technician who may not fit the 'normal' Plus Six profile. I am also aware that a Plus Four demonstrator at KH was also written off but this doesnt seem a regular occurrence like the Plus Six.
The fun in driving my 110bhp 4/4 is that I can drive the car and use all the available power in most road conditions, with a high power car like the Plus Six you can only use a fraction of the available power in most road conditions.
If there was a high percentage of S1 Aeros written off, rather than blame the drivers, maybe there's a point where there chassis just has too much power to be usable in normal driving?