The easiest fix here would be an immunity window, but what we did in our LS was make sure we had tanks and healers in each group then did minimal dps on it while they got most of the threat in. This ensure everyone would get full credit as long as people got their three hits in and didn't pop any dps cooldowns so that everyone had the opportunity to tag the mob.

B Rank changes really hurt our community. People hardly group anymore now, and we have no more need for organization so there's no communication or anything like we had. It's just a mad rush to kill because nobody wants to miss the next A window due to no longer having Bs to supplant what was missed. It's terrible.