I think it's really interesting how the opinions split!
Me personally I do really like Karlie's walk and think it's quite strong.
There have been killer appearances to me like at A.Wang S/S 2010 (8:20)
I agree, that Joan's walk is very robotic.
I think she's trying too hard (see Prabal Gurung S/S 2013) and that makes her look weird and stiff.