I'm not so sure about the first part. If a commander of a deploying unit has higher than 3% attrition rate during pre-deployment training, it'd be considered unusual (with the exception of a jumping unit).
I think even a 3% loss of students due to injuries would be high enough to be problematic for most civilian dojos.
There's also the issue of chronic injuries. Quite a few competitive athletes are ultimately forced to retire due to accumulated wear and tear, and quite a few end up with sub-optimal quality of life after their careers are over.
Now, that isn't unusual in aikido, either. How many aikidoka do you know with bad knees? But my point is that trashing your body now isn't really a great idea if you want to keep training into your 70s.