Wow, that's a long read! Looks like you've been killing it, nice grow. I see what you mean about your plastic pot that red one is almost magic the way that Fantismo grew.
It may be that in your environment with your particular growing style that you will do better with plastic.
To have good success with fabric it helps if you have some type of drain table or something your pots are sitting up on so you don't have to move around early in the plant's development you already know about the damage roots.
I think also it's possible that your Watering your smaller plastic pot more frequently and oxygenating R the rootsoots more fully. In other words maybe you could water your fabric pots a little bit more fully than you are earlier than you are. Benefit the most from The increased oxygen to the roots by frequent watering and of course the root pruning.
It's kind of a balancing act early on especially with soil when you want to lift the pots up to know how much water they can hold.
I like stretchy seedlings starting out I always hoped for at least 2 inches of stretchy floppy seedlings. Then I put two inches of clay Pebbles over the top some people use sand. I like those pebbles better both sand and Pebbles act as a barrier to bugs and will keep our root Aphids and such. Also had the benefit of improved oxygenation and water flow all the way around your pot.
I have a feeling in your tent you would be happier with the air pots since they are plastic and you can pick them up and moving around.
However, if you do stick with the fabric I think you need to water a little bit more thoroughly early on. And utilize some kind of drain table when you're starting your seedlings. I think if you had a drain table set-up and that Fantismo in a fabric pot it probably would have been double the width and about half again as tall.
The Fantasmo was in a 30l fabric pot? I used to stand my pots on wheeled drain tables and found it made no difference for unless I was getting a lot of run off. I feed according to the pots size so bigger pot more water. Also regardless of plastic or fabric pots they all get fed according to the schedule. Daily whilst seedlings and approximately every 2 days there after.
Iv never had a bug or aphid problem
But thanks for all your input.