FFXI actuallly had seven distinct roles, most of which weren't used in regular party dynamics but which came into play on bigger NMs.
In a regular party those roles collapsed into the "trinity" somewhat. On larger NMs, the roles became more granular, and were often duplicated multiple times over. Consider the 75 cap standard Jailer of Love setup: A tank party, with two PLD, two whm, a rdm, and a bard. A DD party, with 4 melee, a whm, and a bard. A BLM party, with four blm, a rdm, and a brd or a smn. An external BLM party with 3-4 BLM and a RDM. JoL was technically killable by far fewer, but the overlap of buffs and healing within the main alliance meant you had a lot fewer scary moments, and putting the second BLM party external helped with hate control. (Oh, there was probably a THF in there someplace too.)
Now pit that against a standard 75 cap Dynamis Lord setup: You have a puller team with a THF and a PLD. The THF's sole job was to run the dragons as far away as they could with flee while the rest of the alliance took down the big bad. The main party was 2 PLD, a WHM or two. You have three bards doing a true bard rotation through the alliance to super buff everyone for a couple minutes, because a couple of minutes was all you had. You had as many DD in the main alliance as you could, then the bards dropped out and healers replaced them, and the bards went up to the BLMs in a separate alliance and sang ballads. And when the NM was pulled, everyone threw everything that they had at DL. When it worked, it was like NASA launching a rocket and it was beautiful. When it didn't work..... well, there were a lot of dead bodies sometimes.
Job versatility is important. I think XI's big issue for many years was that the variety of endgame content didn't permit enough job variety. We actually had a PUP who'd come to Jailor of Love, because his puppet was maxed out for nuking, and the lilttle guy provided a steady DoT of 10,000 -15,000 hate free damage over the course of the fight. The giant jellyfish would have moved if a DD did anything like that over the fight. (JoL was a rare XI fight where positioning of the players and the mobs was absolutely critical.)
Now that XI has multiple tiers of content, easy access content, hard mode content, and every flavor in between, people are more welcome to break out of the "trinity" roles and just do their own thing.