Sniping is one of those things that are allowed but makes you sound like an douche. It's like taking a seat in public; if you saw someone sitting at a spot and they get up to grab something, are you just gonna sit down at the exact same spot and claim it's yours? Technically, the seat is public property therefore anyone can take it whenever they want, and the other party can't do much (or even care enough to do much). But it shows how rude of a person you are, just because you can't utter a few words to ask nicely for the seat.
Most scanlators who are busy will give you the projects if they deem themselves unable to scanlate it further and hurting the readers. Similar to a person who will give up the seat if they don't have a particular reason to be at that exact spot. It's not hard, just ask the original scanlators if they can continue, and if not, you will continue the work for them. From the chapter spam, obviously 15avaughn can handle it perfectly and does not have an issue with time.
Not even gonna get into the whole speedscan and quality vs. quantity argument.