I suspect this is a bot post, but I'll bite.
Onscreen controllers eat screen real estate. In the few games I've played over the years with onscreen controls, the input was clunky and my thumbs got in the way of the action.
Both DualShock 4 and Xbox Wireless Controller (Xbox One S/X and later) support wireless Bluetooth connected to iPhone and iPad on iOS 13 or later. An Xbox controller is perfect for those iOS games with Bluetooth controller support.