After 20+ years of cell phones being in common use anyone manufacturing devices has to realise that the phones are subject to certain stresses, or even abuses, in everyday use. This includes being stressed in pockets, pressed hard against things like tables or chairs when people walk into them and other general abuse. Such abuses have become the norm because phones have been able to take such treatment.
It seems quite reasonable to expect that you should be able to use the 6+ in the same way, after so many phones over so many years have shown themselves to be resilient to such use/abuse. If it's suddenly necessary to treat the phone differently then that would seem to be a flaw in the design. It clearly isn't a general issue with large phones, just the 6+.
Personally I've always treated my devices with great care, including my 6+, and I've not had a problem. The point seems to be that others may not take such good care but It hasn't caused a problem with devices they've owned previously and they should reasonably expect to be able to use their 6+ in the same way.