He may have been referring to my discussion above about mill gap settings and mash efficiency. If you want more detail about the 3-roller mill, in my review link below I have pictures of the different grain crush between 2-roller and 3-roller set at different gaps. As I noted in that review, I could visibly see better crush with the 3-roller mill (all grains at least cracked), and have avoided the stuck recirc I would occasionally get from crushing finer on my 2-roller.
https://www.homebrewfinds.com/2020/04/hands-on-review-monster-mill-mm-3-grain-mill.html
Crush improves the rate of conversion dramatically, and it also reduces the amount of time needed for osmosis to equilibrate the sparge water with the grain particles, but it does create a tighter grain bed and increases the probability of channeling in a recirculating or fly sparged system.
You can get the exact same or higher efficiency with a coarser crush if you mash sufficiently long to ensure 100% conversion efficiency (60 min is long enough). And then sparge slowly enough to allow the sugar content of the sparge water to equilibrate with the grain particles as it passes through the bed (again 60 mins is long enough).
The uniformity of grain particle size doesn't affect efficiency much at all.
Many of my grain kernals in my mash appear to be whole unless you look at them closely and realize they are cracked while leaving the husk in tact. All it takes is for them to be cracked for water to get in. If water can get in, conversion and lautering can both occur.
When I taste them after the sparge there is no detected sweetness so they haven't gone to waste. And I have checked with an iodine test as well, and I routinely hit between 85-90% mash efficiency for an average OG beer (1.050). all good!