I'm pretty sure the whole point of making "return to home" a gesture rather than a tap/press is because Apple wants to eliminate both the physical home button as well as the waste of space with a virtual home button.
If I understand you correctly with your last statement, I assume you're envisioning a system where you would be viewing an app that takes up the entire screen, but by using haptic controls, eg Force Touch, it would return you to the home screen rather than register it as input within the app. But this wouldn't work because it would create the potential for conflicts with how the app developer designed their app. What if there are scenarios within the app where it requires you to use Force Touch in the area where you'd usually press to return home?
The swipe up gesture is the best possible solution because it solves the problem of wasted space on the bottom of the phone, and is a simple motion that would not conflict with any other system functions.