None of them really. The rotation flow is pretty much balanced around the level of the current expansion and nothing feels complete for me until I reach level cap. With anything below lvl 60, all of them feel like a chore to play. Maybe not for SAM and RDM since they were designed for SB and not much buttons were removed when ShB hits. Jobs have been becoming easier by aiding us in resource management via "reworked skills" or "new skills" at high levels. Not having those new skills all of a sudden would require you to remember what you had to do before ShB level cap and it doesn't help when some skills were removed due to button pruning since the initial flow designed have already disrupted.

Example for new skill, a lvl 80 DRG now do not need to be mindful of the timer they have left on BotD when entering LotD because it will go straight to 30 secs anyway due to the new BotD Mastery at lvl 78. Once you get used to that and you are thrown into lvl 70 content, you need to constantly remind yourself to enter LotD at least 23 secs or else you are going to miss that third Nastrond.

While for reworked skill, playing a DRG at lvl 60 ShB and playing it at lvl 60 HW are two different story. Back then, the danger of dropping BotD is real since Geirskogul remove 10 secs off BotD and BotD itself is on 60secs cooldown. However, now and even more so after 5.1, it is almost impossible to drop BoTD unless you are doing it on purpose.

Similarly for BLM, enochian used to be on 60secs cooldown and now it is 30 secs. You get Umbral Soul at lvl 76 as well which would allow you to maintain enochain during movements between monster packs in dungeons or phase transitions.

As much as I love this game, playing a lot of jobs at lower level is usually a snoozefest.