Heavensward and Stormblood content unlocked

I know the MSQ was really important in ARR because basically everything was locked behind completing it. Now with Heavensward and SB is it the same? Or are you given more...leniency because you have the basics unlocked and all it is now is adding to stuff you unlocked in ARR or the occasional dungeon or raid?

Also, would you have to go back to the starting cities to do GC stuff?

MSQ gates everything.

And yes, many activities, including some Grand Company ones, involve returning to starting cities.