Thrustpig, you have it in one.
Of the chaps I know of that are considering venturing on to the 3K gig, the raison d'etre, or at least one of them, is so that they can attain the required hours on the 330. In so doing it does at least two things; opens up all sorts of other opportunities that you have suggested and gets them out of the quagmire of the seniority system that may very well hold them back from a wide body command for any foreseeable future, if at all.
Good luck to them.