Candy clay does work well unless the temperature is high and there is high humidity and then it can become soft, too. Regarding fondant roses and drying, as I said, it all depends on the fondant formulation. My homemade MMF does not take weeks or months to dry. It is dry enough to pick up within 8 hours and after a day or two it is dry enough to be used however you wish. The good thing about fondant is that if you are going to make a large number of flowers it is a whole lot cheaper to use. Also, it is easier to make gradations in color for specific purposes than what candy clay by itself is. I have also found that a fondant/candy clay mixture does not have the same pliability as straight fondant or straight candy clay.
But, as in all things, find what works best for you. What works for others might not be your best option. It just takes trying different things and a bit of practice to find your own way.