Not much to add.  Balance and separation are two very important concepts to learn with discus.  All of this garbage we do is to get more separation and allow for that strong whip at the end.  

It's hard to see here but he is leaning forward slightly with his shoulders.  He won't be able to lead with his hips at the front because he didn't lead with them here.  Also, with the recent reading I've been doing the discus being low here isn't a bad thing.  Kanter is just fairly strict on keeping the discus at 90 degrees (well not that I've heard him say it, he just always throws it that way).

If you look closely you'll see his knee pointed down and the toe pointed at the circle rather than at the field like Kanter here.  This is going to force his hip back rather than open it up.  Again making it more difficult for him to get his hips around leading to an under completion.  He had the habit of throwing off the the right alot. In fact most of my guys did this year. 

I really don't like to focus too much on the block in throws.  There's so much that has such a large effect on how the person moves through the throw that I'm always curious when someone spend more than one practice focusing on the block.  Especially when I see they are way off balance.  Even worse when they are throwing under 100 and the block is the main focus.