Well I see a downside, you can only learn so many movement patterns successfuly in a (hopefully) short period of time. Decide which you're going for and nail it.
For you Hunter I'd say you do want to drill Sumo a lot, and potentially moreso than SLDL. Your form isn't strong enough yet that you could justify doing many (or even any) assistance exercises.
Looking at those videos, you seem to know in your mind what the right position is, but as you pull your body pulls you out of the right groove to complete the lift. So for you in this case, drilling the actual lift over and over will work.
BUT ONLY if the form is perfect. Practice doesn't make perfect, perfect practice makes perfect.
Drill Sumo, at a weight you can MAINTAIN that arch you begin with and build up from there.