I have found a recent paper on free choice feeding for meat birds, to complement those on free choice for chicks and free choice for laying hens in post #9 above
https://www.semanticscholar.org/pap...ewer/f6d0fa455d8cf3c3e942664c46edae5984181a4b
The conclusions are "1. In conclusion, free-choice feeding of free-range chickens resulted in similar weight gain and lower breast yield compared with formulated feeding. 2. Free-choice feeding cost less than the fully formulated diet in this study. 3. Free-choice feeding may be more suited to small- or medium-scale production rather than large-scale production." There is no evidence the birds choose a deficient diet (or excessive fat) from their ability to choose what to eat.
It also observes that "Although grinding, formulating, mixing, and pelleting may have advantages for feed intake or FE, many small producers are interested in whole grain feeding to reduce the energy used in feed processing and also for gastrointestinal health. Whole grain feeding enhances the development of the gastrointestinal tract so it is better able to absorb dietary nutrients, optimizing gut performance [29]. "