This is a large part of the problem with commercial feed. It's concentrated. They get what they need in a very short time, and the rest makes them fat and/or lazy. You yourself frequently mention the need for exercise. They get that looking for food. They enjoy it. They will even forage when full. I can find the refs for that if you want.
The research was motivated by the question of how to get the maximum output with minimum input, in particular, at least cost, with no concern for the long term health of the production birds ('long term' being 2 months old for broiler chicks), or indeed the environmental cost of such production systems such as eutrophied rivers and fields in the vicinity of such a production unit. The wasted excess nutrients in the so-called 'complete balanced feed' given to millions of chickens in its catchment area have nearly killed the River Wye. The marketing claims of feed manufacturers should not be mistaken for good nutrition advice.
Yes sort of but...
Fermentation is a method of concentrating feed it could be argued. As you mention birds that get their nutritional requirements from a supplied feed will still forage but what they forage for may well be more selective, self found treats if you will rather than trying to fill a crop.
What do chickens need in both quality and quantity is yet another debate. A high production breed needs more nutrients than a a hen that lays 200 eggs a year for example. So, it's reasonable to take the type of chicken one has into account. Despite the feed isn't producing eggs posts seen on this forum the evidence suggests that the hen will lay eggs in preference to supplying her own nutritional requirements. So, it's the breed that that's the problem, not the feed.
High production hens need more of everything. Concentrated feeds is one way of ensuring they get more. Looking at feed rather than breed is like looking at the problem with the wrong lens.
Little doubt that the majority of commercial feeds are less than ideal for a chickens health, much like the processed foods we eat. But, it isn't the feed profile that's the problem just as it isn't the nutritional values of the junk food we may eat isn't the problem. It's the low quality and provenance of the ingredients and the methods of preparation.
There are lots of feed profiles. There are feed producers that will make a feed to any profile one requests if one is buying in tons.
Chickens get fat and lazy because they are fed commercial feed isn't true. Chickens get fat and lazy because of how they are kept. A free range chicken living entirely on forage is likely to consume much more in the way of fats then those fed on the low fat commercial feeds, but is likely to be healthier overall.
If a chicken is contained and feed is constantly available then they eat out of boredom much like people do and because there is no motivation or opportuntiy to forage and excercise some do become overweight and unhealthy fat deposits accumaulate around their organs.
The land and river pollution from chicken waste isn't really about the feed either, it's a stocking density problem. Nature is pretty good at cleaning up provided one doesn't overload the system. Half a dozen chicken eating commercial feed on an acre of land is unlikely to cause any problems.
None of the above means I'm a fan of commercial feed. What I'm not a fan of is the keeping conditions. All intensive farming practices generate high levels of polution. it's not so much the profile of the waste, it's the concentration/quantity of the waste. if one fed battery chickens unprocessed top quality fermented grains the polution problem would still exist.
I would argue that lifespan of a chicken is governed more by genetics than what it is fed. What it is fed influences it's health while it's alive but chickens are prone to certain diseases through their genes much like humans and other creatures. That's a breeding problem rather than a nutrition problem and unfortunately the backyard chicken movement is largely responsible for this. The birds the backyard keeper tend to favour are not the high production birds the commercial egg and meat producers favour, but breeding is turning the so called heritage breeds into high production birds because the backyard keepers want pretty and high production.
Many commercially produced feeds use the lowest grade wheat (often sweepings from the milling process with the additives sprayed on as a concentrate) and peas, or at least pea protein. They do this because it is cheap; not because it's the healthiest option. The feed you provide is wheat and pea based for similar reasons and the cheap wheat has less nutriants by weight than the more expensive wheats.
I've chosen a locally grown high protein wholegrain (spelt) in the hope that I can avoid using peas altogether. I hope to bring the feed to a particular profile by the addition of other foodstuffs the chickens will eat in their natural form. They don't like the peas, or the pulses, fermented or not. I'm not trying to produce a cheap feed. I'm trying to produce a feed to a profile using high quality,locally grown, mostly organically certified ingredients that they will readily eat in their natural form.
If the allotment chickens ranged from dawn to dusk I wouldn't be bothering with any of this. Again it's the keeping conditions that are the motivation for tinkering with the feed, not the commercial feed. The chickens in Catalonia were very healthy because they had a wide range of forage, lots of excercise and could choose to eat the commercial feed supplied or not.
The allotment chickens who can also choose how to balance their diet if the studies are right have said a very firm no to peas, but unfortunately don't have the dawn to dusk foraging opportunities.