The guy that I train legs with tells me to "explode out of the hole". That means the same thing as the hip thrust. You're not humping an imaginary woman, your just pushing forcefully with your leg and glute muscles to lift the weight. The heavier u get, the more your back will try to take over, like doing a "good morning" exercise. To prevent this, you have to explode up as hard as you can. Yeah, don't think about using your knees to push, keep your whole body tight so you don't wobble, and push with your leg and glute muscles, like you said. Your second video was a million times better, just don't hump the air and you'll be good! sorry, I love to joke around, it keeps me sane!