So you have all these FFXI classes branching off the classes already in the game? Hardly any of the combinations make any sense to begin with.
Stopped reading there. XI wasn't the only Final Fantasy to have these jobs. They're just classic Final Fantasy class/job names with structures inspired by previous titles. The only reason they don't seem to make sense is because we know so little at this point about the bigger plan of all these changes.

@OP: It's hard to say who would be the better tank of enmity abilities alone as tanking is just as much about surviving as it is keeping hate. Especially since many enmity+ abilities may be cross-classed.