Mountains protecting shin = lake/well/pool of Cultivation's power
Origin of Highstorms = lake/well/pool of Almighty's shard power
Thats my theory anyway.
The Highstorms don't come from the Almighty, they are from Odium. I saw Roshar divided into 3 sections. The far west (Shin) protected/nurtured by cultivation, the central region protected by the Almighty, and the far east the origin of the highstorms destroyed by Odium. Cultivation's area may have been larger but she was pushed westward when the Almighty died.
Odium might have hijacked the highstorm creation system recently, but it still seems to have been the province either the Almighty, or even multiple shards. It's too powerful on too much of a constant basis, and powers all the magic we've seen so far in WoK except probably the Old Magic.
Also, there are two different ways to read this epigraph, one that includes Odium as one of the three, and one that counts him as a 4th. Which way are you reading it?:
11.“Three of sixteen ruled, but now the Broken One reigns.”—Collected: Chachanan, 1173, 84 seconds pre-death. Subject: a cutpurse with the wasting sickness, of partial Iriali descent.
Could spren live off/be an extension of/have a symbiotic relationship with stormlight? If cut gems are better at trapping spren inside them, could that be why they hold stormlight better? I'll assume that most of the spren captured don't have minds/personality like Syl does, there seems to be quite a few different types of spren, some of which are extremely small. It's mentioned in 2 or 3 different places that cut gems hold more stormlight.