Seed: -6213056192259519720
Biome: Desert
Go to coords: -327X, 64Y, 380Z
Face East and begin digging down and forward one block until you reach Y37. Turn around and clear all of the ore one block to the left and right, as well as all the blocks above your path downward. Clear them all the way back to where you began digging, all the way up to Y64 and all the way down to Y37. (see screenshots)

In all of those blocks, you will find about two blocks of coal. (see top middle of one of the screenshots)

I took screenshots of my resulting inventory, minus what it took to make more picks and a very small box house.

I mined for more than 1 minecraft week in survival before I found that coal. In that time I accumulated 35 blocks of iron.

I mined in this fashion so that I could use sunlight to light my mine, since I could find no coal.

Is coal supposed to be that rare in desert biomes (or at all)?

If not, it's likely broken now and should be fixed. It feels very imbalanced, at least on this seed.