You can't shrink it any further with USB-C port.
The lightning port can allow the device to be thinner than MOTO Z.
Lots of people are asking for a thinner iPhone 12.
Shrink it further?
Apple's thinnest iPhone ever was 6.9mm... they've got a looong way to go to beat the Moto Z at 5.2mm...
There might be such a thing as too thin, though.
We expect big batteries, multiple cameras, face recognition sensors, wireless charging, and all sorts of other stuff in our phones today.
I understand what you're saying regarding what might be possible with Lightning. You're right... you could make an extremely thin phone with Lightning.
But Apple isn't chasing the "thinness crown" anymore if you haven't noticed.
Apple has been making iPhones between 7mm-8mm for a while now. So they can surely put a USB-C port in a phone at that thickness.
This may clarify my position:
People keep saying the USB-C port is too big to make an ultra-thin phone.
Yet Motorola made one of the thinnest phones ever at 5.2mm... with a USB-C port.
Do you see how the 2nd statement contradicts the 1st statement?
I don't think Apple will ever attempt to make a 5.2mm phone anyway. But if they did... Motorola proved that you can put a USB-C port in a phone that thin.