I feed my pup EVO kibble, and he's doing so much better on it than he was on his previous grain-filled lower-protein food, and he just had bloodwork done for his neuter that confirmed that he is very healthy and happy eating EVO, and his organs are processing it just like healthy organs should.
However, it's true that high protein foods are not right for every dog, or every yorkie either. Just like not every yorkie is allergic to grains, or corn, or chicken the way some are, not every yorkie does best on a high protein grain-free food like EVO. But of course on the flipside, some yorkies do outstanding on a great quality high protein diet - my Nikko happens to be one of those.
There are also well-reasoned sounding arguments advocating high protein and for low protein, and I honestly can't find an
absolute answer. In dog food, there seems to be much more money dumped into marketing than into solid scientific long-term research, unfortunately. So in my opinion, you just have to decide to feed what you feel best feeding, then go for it. After that, you should watch how your dog reacts, how his temperment may or may not change, how his coat and eyes and everything else looks, how his stools look, and if you want to, it would even be great if you wanted to go get bloodwork done on him after you've been feeding whatever you decide to feed for awhile.
You're on the right track though, and it looks like you're really doing your research as best as possible. I went through a good month or two of obsessing over foods and protein and grains and raw and so on... Now I still obsess a little, and I'm still working on figuring out if I'm going to feed raw, which I really do want to... but at least for the moment, I feel good that Nikko is happy and healthy eating his EVO. I have no doubt you'll find a good food for your dog too, even if it takes you a couple tries. Just reason through as much as you can, and pay close attention to any changes you see in your baby when you change foods. S'all good.
Lauren & Nikko