Ok
#1 Sniping is putting out a release with the INTENT to steal it from an active group this is not sniping
#2 why should they. if they want to put work into translation and put it up on here it is their right to do so or mangadex would not allow it.
just because you and people like you decided arbitrarily that only one group can work on a series at a time does not mean everyone has to follow your arbitrary rules.
More then one scan is often better then one as translation is not an exact science and comparing two works provides better context for the story.
To your #1, I'd say the result matters more than the intent, but ok.
To your #2 however, "why should they" what? Apologise? because they ended up doing something they themself see as wrong. Use the right metric? because the oposite creates all sorts of stunted polls and can also lead to all manners of conspiracy theories. Communicate? if that was what your question was about you must have a sorry life (so I don't think that was the question).
Note tha, both of our feelings on translation redundancy are irrelevent to this situation as the positions of all people involved (which we are not) are aligned.