It is a common misconception that Apple is obsessed with thinness when it comes to iPhones. Since the iPhone 6, each iteration has been thicker:
http://socialcompare.com/en/comparison/apple-iphone-product-...
http://socialcompare.com/en/comparison/apple-iphone-product-...
Apple prioritized camera over thickness at that point. Battery is lower on the list and is mostly addressed by CPU improvements.
IMO it’s frustrating that they are so conservative with a mature product. We waited over a decade for basic waterproofing. Apple has an incredible supply chain, but Samsung can deliver better/more diverse form factors. Example: ruggedish phones.
Apple’s focus is both amazing and frustrating to me. They had and lost an opportunity to break Microsoft clients in business.