There's no EXP difference for level 100-119, and they have stated this. You get level 117 armor for free from Records of Eminence, so there's no reason that you shouldn't be wearing iLevel armor if you are level 99. You get enough sparks from doing the objectives as you level to get all 3 sets to cover all jobs, so it's a bit unbelievable that you had nothing iLevel to wear on a job.