Compared to the brands you find in the grocery store, it IS better. However, there are MUCH BETTER foods out there than RC. If you are looking for convenience, Petco and Pet Supermarket carry Wellness, which is one of the best big box store brands. However, Petsmart does not carry it.
My personal preference are all natural foods (the brands were listed in a previous post), which can be found at small independent all natural pet supply stores. Also, the people at those stores are normally educated on pet nutrition and can help you find the best food for your yorkie. The better quality ingredients you feed your dog, the better off your dogs immune system will be and the better off your dogs health will be and the better off your wallet will be in the end (by not spending so much money on vet bills).
This is the best read I have found on dogs nutritional needs. It is long, but you will learn so much!!!!
http://www.orijen.ca/orijen/ORIJEN_White_paper.pdf