Well, a nice thing of maxing out many classes is that you can pick a "flavor for the day", I arrived at a point in ARR where I just couldnt use NIN for anything ouside Expert roulette because it hit too hard... so I was like "today I feel like being a BLM".

Having a main only means it'll be your "first option", but that doesnt mean you can't have another class overgearing it or equalling it.

There is time, you can build up the 4, or even all the classes. And hell, Im pretty sure there are statics out there looking for Tanks!