As long as we have a mix of both i'm ok with at least some of the NM's being HNM's and being on a longer respawn. Either that or require a pop condition that can't be triggered again by the same person for an extended amount of time (i'm thinking a week).
Or they could make a status timer where everyone that fought the mob (and won) are unable to claim it again until it wears off (with a day or two cooldown). Give more people the actual chance to fight it, and hopefully avoid things like claim bots or hours of waiting around trying to catch a pop time. However they do it, the encounter itself should be harder than catching the claim.

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