I think I've found the source of confusion. When I talk about whole grains, I am talking about them sourced individually, not as a commercial sack of feed (labelled whole grain or otherwise).
There are some commercially-produced feeds in the USA that consist of mostly whole grains. If you open the bag and dump it into a feeder, you see a bunch of grains and some powder.
There are many threads about people who used such feeds and their chickens had nutritional deficiencies. There seem to be two main causes of that:
1, dominant chickens eat their preferred grains and leave the rest, then submissive chickens eat what is left. (Usually that causes problems for both the dominant and submissive birds, but different problems in one group vs. the other.)
2, chickens eat the grains but miss the powder. That leaves them deficient in whatever nutrients the powder was supposed to provide (and the powder is only there because the selection of grains is known to be deficient in certain things.)
The common advice is to get those foods wet, with or without allowing time for them to ferment, so the powder sticks to the grains and the grains are harder to pick through. This advice can usually be found on various forums and blogs, and I've occasionally seen it on manufacturer's website. I don't remember if I've seen pictures of it printed on the bag or not.
For people who read certain kinds of threads, this would be common knowledge (
@U_Stormcrow is definitely one such person.) But for everyone else, it does need explanation.
I have no view on a bag of "whole grain feed" as an option on the shelves of the feed store - anything could be in them. They might not even be whole by the time they get in the sack, given the idiocy of many labelling laws in many places.
For the feeds in the USA that were being mentioned, there are large amounts of actual whole grains in the bag, but there are other things as well.
Corn (maize) is usually cracked. Given that I've seen bantams eat whole corn, let alone standard sized chickens, I do not know why cracked corn is so much more common in chicken feeds, but it definitely is. Some of the feeds make a point of avoiding corn and soy, which also avoids the question of whether the corn would be cracked or not.
Examples of the "whole grain" chickens foods available in the USA:
https://www.kalmbachfeeds.com/products/henhouse-reserve
https://milefour.com/products/chicken-layer-feed
https://healthyharvestfeed.com/collections/poultry/products/non-gmo-whole-hearty®
Each of those pages includes photos of the actual feed, which are similar to photos I've seen on this forum from people using the feed. Some have actual powder for the supplements, but I see that some have turned the powder into little pellets instead.
I can't say whether this fits with your ideas of "whole grain" feeds (probably not really), but it is what people in the USA often mean by the term.