When you pull sumo, one of the keys is sitting back and pushing your feet apart. It you do that on two plates or a surface that has any slip to it at all, your feet will slide. It's not about standing on a platform. It's about standing on a surface on which your feet 'will not move or slide'.
Try standing with your feet at the plates and tell me how hard you'd pull up/push out with your feet if you though one of your feet was going to slide out. Like I said, it's a situation in which you could compromise an adductor. The thought makes me cringe.
fwiw, I have a nice wooden platform for conventional deficits when I feel the desire to do them.