Sure I can agree with that, some fights are made much harder without pallies to bop or hunters to do moving dmg. But dps is such a huge part of wow nowadays. In this specific scenario having 8 boomkins on Kromag is going to make the fight a lot easier. It will break people out of the hands quicker and therefore people will take way less dmg, And overall the fight is going to be shorter because people are broken out quicker and can get back to dpsing the boss.
Now the main reason people want fights to be as short as possible is healer mana. A shorter fight means healers can use their mana more sparingly therefore they can recover from mistakes or just heal the dmg taken better.
The overall point I was trying to make was that of niches. Every class will do something better than most other classes like mages are best at soaking abilities with iceblock and g invis which can be a huge factor in making the fight easier. But there are also other classes who can too (pallies hunters etc) albeit worse because they have longer cds but still they can do it. But spread out aoe dmg (another niche) noone even comes close to moonkins.