Sitting here in Canada, it looks confusing to me. Perhaps if I lived with it, it would be better understood.
The only obvious "grandfathering" I saw for those licensed before 1997 was that people licensed then to drive cars can (continue to?) drive some larger vehicles.
My Ontario licence is good for classes B and M with endorsements Z and X
Those 4 letters let/limit me drive any motorcycle, car, bus, straight truck or emergency vehicle (except heavy articulateds) with trailers to 4500kg (with combinations of air, hydraulic or electric brakes, either standard or automatic transmission) for hire or for personal use as long as I wear spectacles.
In some ways I think your system makes more sense than ours. We have the possibility of a person learning to drive and having all of their experience in automatic transmissioned vehicles being allowed to operate a very large vehicle with a "standard" transmission without any training at all on shifting gears. Also, people of limited expreience and training are permitted to operate commercial vehicles to 13000 +/- kg without a "higher class" of license. The lack of basic competence displayed when they are driving cars would be scary to lethal in a larger truck.
If you are curious about our classes of license a link is at:
http://www.mto.gov.on.ca/english/dan.../classes.shtml Other provinces have different rules and it can be a challenge to keep all privileges when moving between provinces (sometimes even from one to another and then back to the first province). Although I'm not sure, I think most tracked vehicles are considered as equipment rather than vehicles and are thus not licensed and the drivers are thus not licensed as well? I do know of a person who had lost his driver's license for drunk driving but drove his road grader to the job site by public roads without apparent fear of consequence on the principle that he didn't need a license to operate equipment, only to drive vehicles (but I'm not sure if he was acting legally or flouting the law).