The difference there is that they still group like boats together. The problem comes when you group dissimilar boats.
Or you get someone that trys to play the system.
You have the same problem in ORC or IMS. There is always someone who build a boat for the rule and the area that they sail. If I was serious about just racing I would go one design(I can't afford to keep up with formula) but I sail what I do because I like the boat and I race because it is just good fun.