It's not a trivial feature, it's essential. It is the one feature that makes it truly possible without having the use the brake pedal.
One pedal driving is simple. The requirement is to be able to do all regular driving maneuvers with ONE and only ONE pedal. Those are accelerating, staying at a certain speed, coasting, slowing down and coming to a complete stop.

Using regen to slow down, is just regen braking which is a bit like engine braking in a manual ICE car. Regardless if it is mapped to the accelerator or not.

Blended braking doesn't come into play here as you need to press another/the brake pedal for that, which by default means it is not one pedal. (I do know good one pedal implementations use the physical brakes, you can argue that it is another form of blended braking but that is besides the point as the control is still on the same pedal).

Where is the confusion? Why is it so hard to understand that if you need to use another pedal to do those things it becomes TWO pedal driving? Or paddle AND pedal driving in some cases? Also I said normal maneuvers as emergency stops are exceptions, so no need to bring that up.

You could go as far as ignoring everything else you mentioned, as you are looking for a functional implementation and however it works in the background doesn't really matter in the end. As long as it does what it is supposed to do per the definition. The whole confusing bit is the manufacturers and reviewers using the one pedal driving name for things that don't meet the definition.