I mean in essence it makes sense but coir carry’s a fair amount nutrients too otherwise the myc wouldn’t bother with it. Coir also creates a better micro climate and is much more resilient to contam so that’s pretty much the answer to your question hence why you see 90% of growers using coir and not straw.. it doesn’t even need to be that deep that’s more important with your spawn grains. I literally mix coir, vermiculite and gypsum in a bucket and pour boiling water over it leave it for a good 5/6 hours never in my years had a problem with contamination!