When I first started deadlifting, I did what was in the video, those "dropdeads" except with more control. I always started from the rack. Obviously this gave me a weakness off the floor. I finally caught on when I couldn't budge 160kg from the floor but had no problem repping it from out of the rack. I started lifting straight from the floor and chose to deadlift heavy, from the floor 3 times a week to bring it up to par as quickly as I could. It worked a treat. I was allready mentally and technically able to pull 180kg (where I was at the time) but physically I just couldn't. So hammering it from the floor and trying to add weight each time, got it back up to where it should be in 5 weeks. Heavy 3 times a week, still squatting/benching and everything else.
You WILL NOT feel good after this, or towards the end. I probably didn't eat as much as I should've to compensate but I believe it wouldn't of helped too much. Just gotta push through and work hard to get where you want to go. If form starts to fail, obviously take a break, recover and get right back in there.