Let's talk about the challenge log.

[Gemina]

Experience rewards for Dungeon entries in the challenge log are the same up to level 60. Feeling Lucky (3 dungeons via the duty roulette) gives 15% of your current job's current level. Dungeon Master (5 dungeons) gives 10% of your job's level.

My 51 paladin (1,058,400 experience from 51>52) gets 158,760 experience from Feeling Lucky, and 105,840 experience from Dungeon Master.
My 34 lancer, if I were ever inclined to level it given the days of cross-class are over (217,900) gets 32,685 and 21,790.

Except at level 60 the equation breaks.
My level 60 white mage (4,470,000 experience tnl) gets 583,200 experience from Feeling Lucky, and 388,800 experience from Dungeon Master. That seems off.
My level 65 red mage (6,995,000) gets 583,200 experience, and 388,800 experience. Wait a minute.
I asked my friend, and their level 63 monk (5,809,000) gets 583,200 experience, and 388,800 experience.

Any of that seem off to you?

Not at all. One thing to keep in mind with 'Feeling Lucky' and 'Dungeon Master' is you running the roulette three times also registers towards the requirements needed for 'Dungeon Master'. This means you realistically just need to run five dungeons to reap both rewards. I would think of it as the sum of both equal 25% of your job's current level. This is more than fair for a weekly reward.

As for 60+, echoing what another poster stated, the game's experience point system is designed to get players caught up very quickly. By 'caught up', I mean to level 60. This is the level that you start off at in the current expansion and you are meant to work for the exp to get to the current cap. Thus, the most efficient means to get your exp going from 60-70 is to run content in the current expansion, not older content that is meant to catch players up. You're basically penalized for trying to level up this way.

As for getting to 60 with your alts, you should have no issues here. FATEs, dungeons, beast tribe quests, side quests, PoTD, PvP, daily roulettes, hunts, and yes the challenge log too are all rich exp sources to tap from. It's really difficult for me to sympathize with exp gripes when players were already at level cap not even a week into the new expansion.