My thoughts on some of those "benefits":The benefits of the smaller form factor of a 4" are numerous:
Smaller display is less costly
Fewer pixels to fire up - longer battery time (even with less space)
Better heat dissipation
Less prone to bending
Actually being mobile,
Fitting a pocket (the best camera is the one you carry)
Better grip, no over-reaching your thumb
Does not make you look like an mobile addict, even if you are
So I would strongly advocate for going back to a human form factor. When I reach my alien 2,5 meters high and my hands are grown by 30 percent, I might just like the bigger size, but not now.
Smaller battery in a smaller device won't result in better battery life.
Not sure how a smaller surface would result in more heat dissipation.
While that is true, bending really isn't something to worry about with the 7000-series on the 6s/6s+.
6s+ fits in my pocket just fine.
I switched from 4" to 5.5" and am so far really enjoying the larger screen on my 6s+. I'll simply have to get used to more bulk in my pocket.