I always thought this was an excellent video explaining proper left hand technique.
Great video!
But an important distinction, that the video is called "safe technique," not "proper technique."
"Proper" implies a value judgment that only certain players are playing the bass correctly, while everyone else is wrong. Who gets to decide?!?
But I think it's all relative, and no two players are exactly the same. Geddy Lee has the "proper technique" to play "YYZ." Cliff Burton had the proper technique to play "Orion." Chris Squire had the proper technique for "Roundabout." Paul McCartney has the proper technique to play "Taxman." And so on and so forth...