Design patents effectively work like brand protection. They literally only protect new aesthetics and ornamentation. The reality is that the iPhone did start the trend of rounded corner rectangular touchscreen phones. When it first came out, it was a fairly novel form factor for a phone. It didn’t prevent other form factors from being released. Like, the fact that it is now so ubiquitous that we take for granted smartphones look this way is a testament to its success. And, actually, plenty of phones did right angle screen corners. Design Patents are extraordinarily narrow things and, among the many issues with the current USPTO and the US IP system in general, it is probably the absolutely least problematic piece.