Well, there will always be some specific jobs groups will require in them (such as Caster Dps for Ifrit for Nails).

But I like to prove people wrong that my job X is just as viable as Job Y in situation Z. Now, I don't have many Mmo's experience, only 3 (one which didn't have roles, other one was WoW and now FFXIV). When I played WoW, most of the community (and even my guild) said Fury over Arms for Warrior DPS. Funny, even undergeared, I was always in top 3 dps of groups I participated in. Was I lucky with numbers? Maybe. We'll see when (if) I switch to Dps in FXIV.