Here is what I understand from the video.
Torque converter housing is bolted to flexplate. Converter housing is the impeller itself. As the impeller spins, it throws/pushes fluid toward/into the turbine. As fluid hits the turbine, the turbine spins and the fluid flows through the turbine and changes direction into the stator. The stator throws fluid, at a right angle, into the impeller, allowing it to spin easier. Fluid passes through the impeller and around back into the turbine. That creates a cycle.
As the cycle increases in speed, the turbine speed increases, and increases speed in the input shaft of the transmission. At a predetermined RPM, the fluid pump within the transmission reverses flow and instead the pressure holding the clutch plate against the backside of the turbine, the pressure holds the clutch against the housing, thus allowing a 1:1 RPM ratio into the transmission, eliminating the potential for the heat generating speed difference between the impeller and the turbine.
The part I'm fuzzy about is the point of the stator. It increases the pressure into the rotation of the impeller (causing it to spin easier/faster) but not the pressure through the impeller (which would push against the turbine harder). So that in itself causes a speed difference.
Also, where in that does it say how stall speed affects driveability?
His description of loading the engine with your foot on the brake and stalling out at 2500 RPM, leads me to believe that as transmission speed increases, the stall speed should, in theory, increases. So a higher stall would just mean a greater potential difference between engine speed and transmission speed.
So that leads me to think that the only advantage to a high stall would be that you can launch from a higher RPM on the strip, which would be useless in daily driving.
And that video may be enough for you. But he is speaking generally, which is a good baseline. But until I can form a fully functional example to base all that general information on, it's just information.