I tend to agree that selecting stallions as long 2 y/o's may not be in the best interest of producing good riding horses, and many of the German registries introduced lunging a few years ago as part of the licensing inspection process. This way, they can at least get a bit of an idea of how the horse works when he is asked to carry himself through his topline and how accepting he is of contact with the bit, and of how "trainable" he is. The Oldenburg Verband also holds an under saddle licensing, held in spring for 3 y/o's. They were thinking at one point of doing away with the late fall 2 y/o inspection and replacing it with the 3 y/o under saddle inspection, but I don't know if that is still the case - I understand there was some pushback from some of the stallion owners about it.
I do understand, though, why the big stallion stations would rather license colts at age 2-1/2, than at age 3. For the latter, the colt is on their payroll for a longer period of time, which costs them more money in upkeep and training. And, they can start breeding them earlier if they are already licensed by the time they go into their 3 y/o year - esp. desirable for the stallion station if the colt was a licensing winner or premium stallion because there are usually lots of breeders eager to use him.