I always found this a bit hilarious. It's like SE was looking no further than, "What is the maximum rate at which we want to allow soils to enter the game in an hour? Five grade 1, or three grade 2, or one grade 3. Sounds right, let's print it."
The difference is, in order to GET those five grade 1 or three grade 2, you have to spend that ENTIRE HOUR mining, whereas with the grade 3 you need to spend five minutes per hour mining, tops. While a grade 2 miner is monotonously flipping from node to node, a grade 3 miner can run a dungeon, do some crafting, then hit the node.
Yeah, an improvement to yield is definitely in order. I garden with pretty much nothing but grade 3's just because they take so much less of my gaming time to collect!
