I don't think u could get an improvement in root mass n health vs what u did with that pot imo. I tried fabric pots n didn't like how they could saturate out the side n the salt buildup up on the sides. That's just my limited experience with them. I'm not necessarily against them, just not sold on the better effectiveness they r supposed to offer.
It is not about more root mass it is about preventing the circling and root bound like growth which airpots/fabric do by letting the root tips be exposed to air so they basically stop growing, thus preventing the circling and excess root mass. He has way too much root mass in that little pot imo and if growing varieties with autoflower tendencies when root bound (i.e. sweet pink grapefruit) I would be wary. I know that you can have way more root mass in coco, but his seems excessive to the point it would effect even draining.
Plastic pots also have holes on the bottom allowing many common pests to hide such as fungus gnats. In my area those are a big concern and I know they thrive in coco from my own experience as well. Switching to fabric pots allowed me to treat them much easier.
You can also eliminate 90% of your time watering in soil by using a capillary action water system, which can be a constant or periodic source. As a result vacations are cool again and you have way more time to actually care for the plant...I would love to see if I could accomplish that in coco too someday.
I can see the salt build up concern, but I have no input on that and would be best answered by a master coco grower.
The only thing that kept me from switching over to fabric pots for so long was price and not wanting to make my own. Having sourced cheap ones now I no longer have these reasons.