Wesk Alber's poll on Jobs

[Absurdity]

I mean if they are so casual they are playing SGE like a pure healer why do they “need” a healer at level 90 for roulettes over any other job (say a tank if it’s a matter of queues)

This group of people that you are referring to just doesn’t make any logical sense as to their existence

Because tank queues aren't actually that good in Endwalker. Even when tank was the supposed "adventurer in need" it still took 15 minutes for the queue to pop, whereas healers got instant queues.
But adventurer in need provides bonuses that you might want to take advantage of anyway, so having one of each role is beneficial.