I can't really speak for Street Fighter V, but I can say that Easel would assign command delay to the person who is introducing it. So if a person is somehow forcing their inputs to arrive later than they should, they would be assigned more input latency so that the other players would be unaffected. Easel also has a lag spike protection system where the server will just forcibly reschedule inputs if they arrive really late for some reason.
Yeah, most of these are relatively solved problems, but they are nontrivial enough that one of the industry giants couldn't get it right on its first few tries.