When you look at the strongest DLer, they lift more like the photo of Lani on the left. That is FAR from a weak start, IMO. With your legs less bent, you're stronger (that's why you can partial squat and DL way more than full range movements). With the form on the right, you are putting much more emphasis on your legs, and LESS on your back, glutes, and hams. If you watch the big PL guys DL, they have their shoulders over/slightly behind the bar at the beginning, and they squeeze the weight up, wedging their thighs under the bar as it goes up, and driving the hips forward as their legs straighten.
This weak start analysis is just plain wrong. You just need the strong midsection because when your spine will receive more of a shearing force when you are bent over forward more. Just like RDL use the posterior chain more, the DL with less leg bend will need more butt and back power to complete, but you are in a better position to recruit it with less knee bend. Much better leverage. Prying vs. lifting.
There was a great DL video of Brad Gillingham pulling about 850# the other day on a strength site. I downloaded it to my home computer, which I don't have access to now.