I came to say this. It's not speed, it's comfort. I've been using Dvorak on my Kinesis Advantage since mid 90'es [1]. I don't actually think Dvorak is the best possible layout, but as the video points out, we are already in the realm of diminishing returns.

[1] I still use Qwerty on non-Kinesis keyboards and this fact is enough for my muscle memory to eliminate any mental overhead of switching.