Unfortunately, for participating in endgame, FFXI is a game where specialists are useful and "hobby jobs" are not. Any job can be considered useful however when doing lower level activities but from an endgame standpoint, jobs like pld and ninja are the only jobs that have defensive capability and jobs like sam and war are the only jobs that have offensive capability. White mage is the premier healer in endgame. Bard and red mage is extremely useful in all situations. Jobs like pup, thf, and dnc are mostly just hobby jobs that are useful in lower level situations.
there arent that many good pups because of lack of understanding of the job. but PUP like many other jobs can b usefull in end game. not long ago DRG was the "lol" job and nobody wanted it. as more people show what a job can realy do then you'll find a good use even for endgame. THF is a must for most endgame. and a pup can DD non stop and w/o hate and perhaps even better than a BLM or most DDs
To the author of that 2nd paragraph. THF is a must in endgame for drop rates, any other use of a THF would not happen if not for treasure hunter. BLM and PUP are not really comparable, as they are not used on the same enemies. Magic damage and physical damage is used very distinctively in endgame situations, and PUP has poor magic damage, even with a caster frame.
That being said, any job can be very useful in the right situations. I've seen many a BST out-parse a WAR. Regardless, if you have it, you'll still be asked to come as SAM. If you really want to be useful, then have a job for every role. That way you can be included whether the group is short on healers, dd's, or tanks.