Chains took a long time to build in Abyssea and it wasn't so well suited to just quick bursts of levelling like FATEs are. At least FATEs are fairly constant XP from when you arrive to when you leave. And it was in fact Abyssea was far more tedious because you usually ended up in the same spot fighting the same things for 3-4 hour at a time, no variation, only moving as far as the page NPC and back. And then you had the fell cleave parties with 14-16 leeches. I like that FATEs require active participation and you can't just cap a job whilst AFK.