I would personally ignore the people that likes to cry "sniping". I have no issues of multiple groups doing the same manga. I like to see peoples interpretation when they translate and their wording choices.
100%. The entire focus on "sniping" in the scanlation scene came about because of groups like Jaimini's Box and Champion Scans and similar that were trying to make scanlation into a patron-supported business for themselves, rather than a hobby they did because they enjoyed it (and often were honing their skills so they could then put them to work later, too). If other teams or people gave their own iteration of a chapter, then it would reduce views on their websites, which would reduce views on their ads, or lessen pressure from their erstwhile monopoly since they also preferred to keep the latest chapters held back for those who paid for them, as well.
Pretty sure they have a rule against sniping
No, Mangadex do not. People have cited a commonly-held standard of scanlators (formulated primarily to deal with those who scream about sniping) of waiting several months before assuming it's been dropped and can be picked up, and then assuming that Mangadex adheres to it, but there is no such thing. They DO have a policy against substandard work, however, which a lot of "sniping" chapters are, which may have led you to believe that they follow such, as those chapters are taken down for their lack of quality, not because they are "sniping".