Sure melee gets raidspots, but there are many raidfights with maximum melee spots, while you can count the amount of fights with maximum ranged spots on one hand.
And while i do believe they don't do that with some anti melee intention in mind, they have to be aware of how that will turn out when they make "can't stand within 10 yards of another player" bosses. I don't mind it on a boss like n'zoth with the sucks you to the boss mechanic, but on something like fetid devourer it's just stupid design.
it's not been that bad in BFA though.
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Theres plenty of mechanis in the game with hidden conditions like "always goes on ranged unless there is less than 3 ranged" or "doesn't target healers".
just make something like that so it's always possible to have 6-8 melee before the mechanics actively punish it. or you know, just don't make mechanics that by their nature limit the melee spots in the first place (and there's a difference between melee unfriendly mechanics, and melee spot limiting mechanics)