No such thing as scraping your knees too hard. I've found the best thing to do is to actively drag the bar up your legs from the floor upwards. Long socks are pretty much essential.
Your pull looks pretty decent to me, but a video of you pulling close to your max will be much more revealing in terms of what you need to improve on.
Also, don't worry so much about lowering the bar so slowly. As long as you don't drop it you should be fine, unless for some reason you're deliberately training negatives (IMO not a great idea for deadlifts).