Sorry replying the old thread. But, is the case still mandatory, given the back and front glass (in 11 & 12) are now stronger (according to Apple and some drop tests in YouTube)?
Whether Apple claim the glass is tougher or not, I think you’d still be very lucky for it to survive a drop with no damage. I wouldn’t even think twice about putting a case on an iPhone and certainly don’t conform to the notion of paying Apple for additional expensive insurance policies.