Jobs are supposed to be party role specializations for the classes. So yes, pretty much all of the classes will become obsolete in parties with the jobs around.

Going one-to-one with classes and jobs actually isn't an awful idea. This way they can keep introducing new classes (and weapons/fighting styles) and have each one with a job for it.

So since we've only got 2 mages for the whm/blm jobs, where does red mage go? Fencer. In some FF games (FFTA/FFTA2/probably more) Red Mages use Rapiers as their main weapons. What other job would there be for Fencer really? Turning a strictly melee class into the proper jack of all trades melee/magic hybrid.

There are dozens upon dozens of Final Fantasy class/job types they could include. With it being one-to-one they will just have to keep adding more classes which means more jobs too.