Something I laughed about on my first viewing also; but I think they chose this specifically. If you watch through the trailer you'll notice that none of the characters actually kill any units. My guess is that the KO animations and surrounding visuals aren't done, or they just didn't want them in the trailer, so they purposely make Edelgard not kill the unit.
I'm keeping an open mindset. I encourage IS to continuously try to improve their work, so if they try new things with battle formations, extra units around main ones, etc. I'm all for it. The only thing I genuinely don't like is the cut scenes look choppy and uninteresting; I was hoping for some Fates-tier work, but these look low budget. Not at all what I expected for FE's return to home console.