Well, as Leatherback has already said many times and against all modern bonsai theories, bonsai trees can thrive in organic soil.
I have just came back from a nursery where the japanese father of the owner kept JBPs and JRPs from seedlings he's brought many decades ago from Japan. After he passed away, his son takes care of the business.
And there they were, wonderful very thick and old big pines in japanese bonsai containers and...
Organic soil.
Yes, I have questioned. The answer?
"We fertilize. We decandle. We prune. And we water less than the new growers. But we water when the trees need."
And they were thriving, after almost 100 years.

My personal take is since trees in nature can grow in different soils so its same with Bonsai. I think its just two different philosophies and approaches, may be one is older and one is newer. My personal observation is that trees grow faster in inorganic grained substrate while in thick organic soil they go slower. And of course when you have your tree ready after 40-50 years you just want to have it going slowly and steadily so organic soil will be a better option for that. IMO.

I do use organic soil, but as a component of my soil mixes. I do not use it completely and as a single medium in which potting my trees.

I´ve, as Spacewood previously said, found that trees seem to develop better in a varied soil mix. Actually the trees that I´ve lost have died possibly due to an ineffective substrate, almost completely organic, at the moment of obtaining them. This combined with the fact that repotting time had already passed... Well the ending was near for them.

Although, I also admit that my feel for the trees´ needs have improved and I must also acknowledge the fact that now I take better care of them. So, who knows... Maybe a couple of them would have made it if it had happened today. But, in any case I prefer to balance my soil mix.

Alain

You knowmy view. Modern coarse substrate make it easier n us; You can water almost as much as you want without hurting the tree. Which is why I do not protect my trees in a country that has 6 months of wet dark winter. And so far, this has not cause me headaches.

If I have them in organics, I would have a hard time keeping the oil reasonably aerated. But in other climates, where summers are long and hot,a high level of organics is called for. In the end it is all a balance of the care yo ucan give, the location you are at and what a tree is accustomed to. Many trees in the wild grow in near full organic, dense substrate and survive. (Main difference is that we have a MUCH higher density of roots in our pots, so need to cater for enough oxygen exchange).