Seriously, how...

[Lemuria]

Hit lvl 56, start spamming blue scrip turn ins. Infinite allowances+the exp you get from crafting the turn ins.

Sadly, this is almost the single most inefficient means of leveling up as well. The average collectible hand-in is worth about 100k at level 56, with highest quality, you might squeeze out 120. The average levequest is also worth 120k, with a double bonus for HQ, making it 240k. The GC hand-ins, which can be done only once per day, can range from anywhere up to 1.6 million XP for a starred HQ hand-in.

So, yeah. While you can do tons of blue scrip hand-ins, you'd have to craft a significantly larger number of items to pull this off, so it's only for those who have a lot of gil or materials to throw away.

Note I attempted to HQ each getting the 300% XP bonus.

A minor correction, HQ hand-ins are worth double, not triple. This was reduced long before Heavensward was released, and the base experience for the leves increased at the same time to compensate.