Upon closer look at your pictures, I may have a solution. I would try this with one plant and see how you like the results, I by all means don't claim to know everything and I learn new stuff everyday, but I've had great results with my plants so far so take it with a grain of salt lol
In my opinion you are in need of a good pruning. I can see some dead/dying/yellow leaves in the pictures. Cut them off. Any portion of a leaf that is dead, prune. If it's just a portion of the leaf, cut off just that part if it's less than 50% of the leaf. If it's equal or over 50% remove the entire leaf. If a leaf is cause shade over a bud site, remove leaves until that bud site has direct light. This should help with not only your root issues, but your growing issues, as well as provide a larger yield. Again, don't take this a law and perhaps try with just one plant first, but I do this with every plant and love the results.
As far as I know, the reason this would help is as follows. This explanation is of course not meant to be scientifically correct, just simplified and understandable. Anyone feel free to correct me if I'm mistaken!
When our plants are damaged, they concentrate energy energy on repairing (leaves, stems) or protecting (bud, seeds) the damaged area. This we know and is the reason lst and hst techniques work.
We also know that the damage caused by many of the issues are plants may face is permanent. Simply looking at any of the "Plant symptom check lists" available online will confirm this as many state the damage won't ever be repaired, but to watch for new growth.
The root system provides a majority of nutrients needed by the plant. The more nutrients the plant requires, the larger and quicker the root system grows to accommodate the needs of the plant.
When dead, dying, or damaged foliage is present, the plant is constantly trying to repair it. We know it's will to survive is so strong it will grow opposite sex reproductive organs just to insure it's survival (turning hermie).
In nature, it has to deal with fluctuating temperatures, humidity, light levels, insects, animals, pollution, humans, etc etc. So it grows tons and tons of leaves, stems, roots, bud/flower sites etc and has the entire ground in which to grow it's root system constantly searching for water and nutrients. All this in an effort to lessen the odds of eradication in the event one of the previous issues arises. Obviously in a controlled environment, all those extra leaves, stems, and roots, aren't needed and we are allowed the ability to use them to our advantage.
Assuming everything I just listed is correct, it follows that any many damaged or dead leaves, especially those with over 50% damage rate, will never recover to be vibrant green healthy leaves. Yet the plants' will to survive will not let it just stop trying to fix those areas. Basically they will become a constant drain of energy and resources. To cope with the constant drain the root system must increase in volume. If the water, nutrients, and space aren't available to accommodate the increased root mass, root bind, out growing the pot, stunted growth and other issues may arise ergo a smaller, thicker, lush plant with a massive root support structure. Pruning damaged areas and unnecessary growth will in theory allow the plant to use a small amount of additional energy to "cap off" the cut area, and then re-direct that energy towards growth or bud production depending on what stage your plant is in, instead of constantly sending more and more energy towards a damaged area that will never recover enough to be beneficial.
Think of the human body. If you're working on a project and get a small cut on your arm, you spend some time cleaning and dressing the wound, bandage it up, and continue working. Little down time and energy is directed towards the damaged area. On the other hand if while working on a project you break your arm in 4 places, obviously considerably more time and energy is devoted to the damaged area, even though the Dr. tells you you many never have full finger movement again. In a humans case you hope for the best, and try to heal. Our plants do the same although unlike us, they have the benefit of being able to grow new "arms" or "fingers", which they try to do anyways while also trying to support the broken arm/fingers. If we remove the damaged arm/fingers the energy is redirected. With time and practice we are able to utilize these feature to our benefit resulting in healthier faster growing plants and increased yield.
I really hope this all makes sense and helps you out. Like I said before I do not claim to be an expert, nor am I trying to explain this scientifically. This is what I've done with any plants I've grown every since my first grow years ago in which I was to worried and nervous to prune or mess with the plant much and upon seeing the end results of that first grow, was convinced that things could be improved. Never looked back and my ladies love it. Hope this helps!
