I don't have much experience with FFXIV, but in general I like healing and DPSing in most MMOs. Tanking, while of vital importance to the team, doesn't have many opportunities to shine or push themselves, or compete for some level of character mastery. As a healer or DPS I'm always trying to top the charts. A lot of games put a lot of restrictions on what a tank can actually do, as well. In most cases, no matter how good at your job you are, a tank's survivability depends mostly on his healers. Meanwhile a crazy good healer or DPS can actually change your approach to a fight. Back when I played WoW, my second raid group had 3 phenomenally good healers, I healed on my Druid at the time. We were good enough that we could completely ignore a lot of fight mechanics just because we could successfully heal the shitstorm. In my primary group where I DPSed, we reworked a lot of our strategies around the fact that our hunter and I could collectively put out as much DPS as the rest of our group combined. Whenever I got stuck off tanking a fight on my DPS character, I was always bored out of my mind, because there just wasn't really anything like that where I could push myself or think up a better build or more efficient rotation to improve my performance.