My fatalistic .02 cents is that it's not if your going to get injured kitesurfing. It's when your going to get injured kitesurfing, and to what degree. If you've been kiting long enough, you've suffered some form of ding, scratch, tear, or break. I don't think a lesson three or four years ago would have helped Kevin that day. Realizing his limits may have helped. I'm not defending Kevin, but at the end of the day, no kite lesson can train you for a kick in the nuts.
However, I do believe that lessons with the right teacher do benefit a new kiter. (I've seen so many kook "instructors") Sadly, many so called "instructors" are all about the money grab and follow on gear sale from tourists and kooks and don't really "teach" much at all.
Part of the problem is that IKO and the like require little from their instructors other than some money every year. There really is very little oversight from these bodies. In diving, PADI takes the money every year alos, but there instructors do actually have to be able to teach skills. IMO, the same can't be said for IKO. There are instructors out there that can't self launch or land.
I learned how to land a parachute jump in the Army through repetitive drills over 20 years ago. To this day, I can still do a PLF without thinking about it. When I learned to dive, my instructor did basic things like shut off my air supply, and remove the regulator underwater, so I would know what it's like.
I've been kiting since 2002. I'm a self taught kiter, mainly due the lack of tuition where I learned to kite. However, I have observed instructors in popular schools in places like Egypt and Fuenteventura and I believe that kitesurfing instruction curriculum needs, among other things, to add repetitive drills that build muscle memory and intuition. (i.e having people disconnect while actually under load).