Royal Canin (some types) have made lots of Yorkies very itchy. It would not be my first choice for a Yorkie nor my last.
About the corn, I don't really mind it too much. It may be cheap but it is also a great source of energy and linoleic (the oil fatty acid that dogs need to consume). Is it digestible? I guess it should be grouped with other grains and if you don't think that grain is digestible enough, go with grain free.
Apparently beef, wheat and dairy products are the food intolerances most reported by vet dermatologists. At the same time, soy is probably on that list somewhere. So if you want to avoid all ingredients with a higher incidence of reaction, all of these would need to be avoided.
I don't put any emphasis on breed specific food because two different breeds can easily do well on the same food. Glucosamine is added to Yorkie-specific food probably because of their likelihood of having LP. Great idea but is that really in a therapeutic dose? Is it from the correct source? If yes, it would be expensive. I would sooner give Cosequin and know for sure. Higher proteiin has never been shown to cause kidney problems but the amount should be lowered if a problem comes up. While I don't think high protein is necessary personally, I don't think it's a big deal either. It's an expensive energy source but if that's what you want, that's fine.
While I cannot give actual studies of the risks of ethoxyquin (because evidently it's never been proven dangerous in the amounts that are put in pet food), I personally have a big problem giving my dog a chemical that is banned in other countries. I also don't like BHA and BHT and try not to eat it myself. Why would I give it to Ellie?
Dogfoodanalysis is a good starting place to look at ingredients but just because they say something is good or bad does not make it true. And just because a vet sells something does not make it a good product and it does not make it safe (like the lepto vaccine for Yorkies, some forms of heartworm meds that should be avoided, etc.).