I agree that there are many overweight rabbits today. However, I would say that obesity is more often due to improper feeding than protein level. It is not the protein itself that makes rabbits fat, but the amount of feed fed in relation to a rabbit's workload. For example, look at your average pet rabbit fed Oxbow or other lower protein feeds typically sold at pet stores. Many of those rabbits, despite being loved by their owners, are overweight. They simply don't get enough exercise to justify the amount of pellets, whatever the protein level, that they are fed.
Then look at many show and meat rabbits fed more commercial-type feed (Purina, Kent, Pen Pals, etc.), with higher protein. I show rabbits regularly and see many different breeds from many breeders on the show tables. Yes, some of those production rabbits are overweight, but not nearly as many as the pet type rabbits I see, which are generally fed low protein pellets (if they're fed pellets at all). I've used both 16% protein and 18% protein feed in the past for my rabbits. Some gain weight more readily than others, but they can always be brought down (or up) to a more healthy weight by changing the amount of feed, not decreasing the protein level.