While I can agree that not everything should be about stacking and spreading, we do have other fights that present somewhat different ways to handle mechanics. Chrysalis has a mechanic similar to Fire/Ice which we broke down into Stack and Spread because controlling it via the fire is easier than having the fire go out and everybody with ice going with them. (I'm speaking on the orbs that pop up that you have to 'catch' in an alternating pattern so the boss doesn't wreck you with damage (the consequence))
And MEX is only 'boring' as a tank if you're not following Tailturner and Woolywart since they don't use AOEs to do damage. They are unavoidable sources, and if they pick up something like 5 stacks because you weren't paying attention, there goes one healer... then a couple DPS to Mog Rain of Death... then yet another healer because while running to get their partner you died, so now there goes Wonderwall to go wreck his day. So the other healer possibly doesn't even get the raise confirmation, and there's your wipe. And who's to blame for Tailturner having too many stacks from the King?
But I think new stuff IS coming. ARR was supposed to be the baseline, as much has been said. But the fact that we have mechanics and we show up to these things to engage with the fight is a farsight better than WoW Raiding back in Vanilla. Steps of Faith and Chrysalis give me some hope we'll be seeing even more varied mechanics in Heavensward. But both of those fights got a large contingent of people complaining that they were 'too hard' (when indeed, all they really are is different.)
So I suppose at the end of the day what we have is a group of people arguing basically the same point. But one who is getting defensive that they don't want SE to take the only source of real challenge in the game away, because that's what they're so used to hearing on this forum, and the other group that's saying that they want to see more variance in the challenge. I still think if you focus only on player positioning as the only real source of challenge it's the only thing you're going to see, but suggesting that it's the ONLY source of challenge in Binding Coil at all is sort of a far cry too.