Why chicken shows up in so many dog foods
Chicken is one of the most common proteins in commercial dog food because it's a lean, easily digestible protein source that most dogs tolerate well — not because it's inherently superior to other meats.
That popularity is also why chicken sensitivity is one of the more commonly identified food intolerances in dogs: the more a protein appears across a dog's diet over time, the more chance there is for a sensitivity to develop. It's not a reason to avoid chicken by default, just a reason to keep track of it in your dog's food history.
If your dog has been diagnosed with a chicken sensitivity, it's worth checking treats and chews as carefully as main meals — chicken-flavoured or chicken-based extras are common even in products that look unrelated, like some dental chews and training treats.