Infrared gun and oil temp gauges show a solid 40 degree difference between ambient temps and oil temps when plugged in for two hours. This is a fact. Furthermore, the 7.3 Powerstroke drains very little oil back into the pan. It has multiple oil pumps with anti-drainback valves, and holds a great deal of oil (more than a gallon) on the topside of the motor, in the HPOP res., in the oil cooler, and in the oil filter.
Everything is relative. All the way to the point of being a non-issue like your suggestion than the block heater does not provide enough heat to properly heat the oil prior to starting.
You yourself noted that
With a mechanical pump it will slow you cranking speed significantly trying to pump very cold oil
So which is it? You are talking in circles just to argue a non-point.
Is the oil being heated by the block heater or not?
The primary engine lubrication pump sure as **** isnt in the oil cooler where the block heater is. Its a gear pump drived right off the crank, on the front of the motor. If crank speed is any indication as to oil temp (your suggestion, not mine) then the block heater IS heating the oil. And not just the oil near the block heater. The low pressure oil pump pulls oil straight from the oil pan.
BTW, T6 Rotella has a pour point of -41 degrees F, and excellent flow at -30 F.
In other words, at 20 below or warmer (relative to this discussion) is not a problem. Block heater usage as intended by Ford, is nothing more than a starting aid. Not a requirement.