RDM is quite a bit different from the previous game and enters in territories such as Mystic Knight and so on
Actually not really. Enspells are the only thing different, otherwise RDM is ~exactly~ the same as in FFI, FFIII, and FFV. If you doubt this pick up the GBA / DS versions and find out. Their cheap and relatively easy to find on amazon.

That is actually the problem with FFXI now, SE focused too much on keeping RDM like it was in previous FF's. RDM has always had white magic but not as a good as WHM, had black magic but not as good as BLM, and wore armor and swords but not as good as Fighter. You were limited to four members and whatever jobs you chose you had to stick with, for this reason the RDM typically replaced either the THF or BLM. In III and V you could class change so you had a bit more personal choice. I liked RDM as it was good at clearing out ash & trash mobs during the dungeon exploration portion and could switch to buffs / debuffs / healing during the dungeon boss portion. In FFV RDM was the same although severely limited to level 3 magic which made the job virtually useless after midgame. At the end of FFV all jobs paled compared to freelancer / mimic which gained the powers of all mastered jobs and thus was radically overpowered. For a good portion near the beginning to middle RDM was useful as you could switch out the "sub" ability between battles.

Those idea's are great for console RPGs as it allows the players to experiment and play around, they don't work for a MMO because nobody will accept less then "optimal". Instead of (Fighter / Thief / Red Mage / White Mage) you get (Fighter / Fighter / Fighter / White Mage). The first group is my favorite to play, the second group is the absolute easiest to win the game on, so easy you'll think the game's a joke.