Try skipping the extreme smoke mode/ low temp and kick the heat up from start to finish. Every one of the foods you mentioned I personally would cook hotter and faster, 275* or more. I know others here get good results with low temps on the leaner meats, but I save the 250* and under temps for ribs, butts, briskets, etc.

Unrelated to the leather skin question, I take chicken thighs to 175-180*. Unlike the breasts, they are better at that temp and won’t be dried out.

It sounds like you're experiencing a common issue with the smoker, which is forming a leathery outer layer. From my personal experience, the key to avoiding this is to maintain proper moisture and not over-smoke. Try spritzing with apple juice or broth and keep a closer eye on the cooking time. 

Funny that you mention leather, because it's actually my favorite material! I love the durability and unique texture it offers in various products. Leather's toughness might not be great in your smoked meats, but it's perfect for bags, jackets, and other accessories. If you ever want to understand more about leather grades, you can read more about leather in this article from https://vonbaer.com/blogs/blog/leather-grades/. Good luck with your next smoking session, and I hope this helps!