Glomalin was only discovered in 1996 and it contains up to 30% of soil carbon! Fungal cell walls degrade into a sticky product that makes the soil more loamy. Glomalin levels are strongly correlated with soil fertility.

https://en.wikipedia.org/wiki/Glomalin

I think artificial supplementation can be greatly improved, as you suggest. However, it increasingly looking like the soil biome is directly responsible for plant productivity, rather than only indirectly assisting in nutrient transport.