There are many ways to beat the content, but no one knows about them because the playerbase sees how the Japanese or BG does content and sticks to that, AoE damage (with the new actions) GLA uses thier AoE def+, melee come geared for the occasion.

Magic damage restrictions doesnt make mages useless, they heal or buff.

I remember in FFXI, (I know dropping the FFXI card) we went to dyna and mobs would spam AoEs and guess what we meleed, with everyone on the same mob, we didnt say RNG onry so your out of AoE.

DH can be meleed, I was doing it a few hours ago, but people dont want to.

I see MRD and PUG at ifrit, so no there isnt one way to do it, you just need smart players that can adapt to the situations.