I suppose that I need to start over, as I'm not misunderstanding the difference between a Slave Unit and a Non-Powered Unit nor am I misunderstanding any terminology.
It's really quite simple: Older offerings of MTH F Units (F3s, F7s, FAs, etc) that had been sold as sets (ABA) distinctly had the Non-Powered A Unit wired as a "Slave" to the Powered A Unit. Meaning that this Non-Powered A Unit did indeed have a motor, yet it would not operate unless it's tether was connected to the Powered A Unit (either directly or through the Non-Powered B Unit). This Non-Powered A Unit was not free rolling and, again, would only operate if tethered to the Powered Unit.
My question is simply: Are the newer offerings of MTH Non-Powered F Units that are now sold separately (not in sets) still Slave Units? Or are they free rolling and not needing to be tethered to a Powered Unit in order to "roll"?
It's quite clear that you are, indeed, misunderstanding the terminology. If it's got a motor, it's a powered unit, whether it can run by itself or not.
A slave unit can be a number of things:
-a powered unit that must be connected to the master to run
-an un-powered unit that needs a tether to control lights/couplers/smoke/etc
-needs a tether, but can either be powered or non-powered
A NON-POWERED unit can be tethered or un-tethered, depending on what is inside it, but a NON-POWERED unit is always free to roll.
The word "powered" means it has motors and can provide force to move a train, not whether or not it has electrical power going to it. It has nothing to do with whether it has a tether to provide electrical power to it.
The word "power" in the title of a powered unit refers to motors that provide motive force. A non-powered unit has no motors. If it has no motors, it is free to roll.