Hello! 🙂
I have downloaded and tested several "multi-touch test" applications, and tried them on my iPhone 7 Plus (256 GB AT&T Jet Black) . The results were 5 max across the board. This cannot be confirmed nor denied as pure fact, as these programs are not the final word as to the maximum number of touch inputs the iPhone 7 Plus's Capacitive touchscreen can process simultaneously. 😐
I can conclude that this is not a hardware defect, nor is it specific to your device, as seen by our identical results. I would not stress about it, 10-point-touchscreens are really only appropriate in larger devices such as tablets. 😕
I hope I helped! 😝
- Ice Studios