Wow - does your uke have any clue how easy it can be to get hurt if they don't know what they're doing?
I will say that there does seem to be a lack of understanding from the lower grades of why things are done the way they are. - Part of it is the fact that a couple of them show up once a week or every other week. - so if Sensei tried to explain 'whys', etc. they missed it.
I will add that I have been hurt once by a senior student when he tried out a technique - that we werent supposed to be practicing - so I was unaware of what was coming...I think this helped to wake him up a bit. (hadnt had a repeat incident.)
Also, with a guest student, his style was using big 'jerky' movements, which left my elbow hurting for a couple of weeks.
This is excluding innocent accidents, such as when a fellow student of similar rank over did nikkyo and left my wrist in pain for awhile. (That was pure accident...nikkyo seems to be a 'hit' or a miss.)