Opinions & experience inquired - Layering diff. substrates - A good or bad idea? Pure living soil seems better so far, might it work better in bigger pots?

I have played around with layering, not quite the way you have done it, but not too far off. My living soil was doo dense, so I added coco and perlite to it to lighten it up, but was worried about it still getting too saturated in my larger pots (regular plastic, not fabric). I put a layer of coco and perlite alone in the bottom inch so the roots that got there should never sit in stagnant wet soil for long and I added another layer around the middle also about an inch so when the plant is young it can easily access airy pockets easily even if the living soil is a bit on the wet side. It worked quite well and after the plants finished, I saw their roots had spread more strongly in those airy layers while still having access to the nutrient in the living soil. I think your concept is fine, but I would maybe worry about the ratio you have of living soil to inert medium. If the plant stays small it should have enough food, but if you grow a bigger plant, you might need to start feeding more seriously than you normally would to make up for the lack of food. It will also probably dry a lot faster, so you'll have to water a lot more. Not a problem, it just seems it is going to make you work harder for the same result. I'm not expert and some of the things I've done may be really silly, but it worked for me and I grow large plants in those 30l pots without any problem. I just top dress with compost at the start of flower and use FPJ's I make myself and some epsom salt now and then. I would personally move the sand down to the bottom 1/3rd or 1/4th and have more living soil and less inert medium, but try it out and lets see how it goes.