This was only required because they started selling very camo-like player skins which nobody wanted, and didn't even fix the issue very well. people just had to accept it, and I still regularly see some skins blend into the background way too well...
I'm guessing the issue is that this is a supposedly cosmetic item you can buy with cash, so if it has an impact on gameplay, it creates a pay-to-win environment.
The gameplay is quite complex so that difficulties parsing enemies due to visuals just detracts from the experience and reduces that gameplay complexity. There are still situations where it's intentionally more difficult to recognize enemies, but that's an explicit choice made by map designers, not an accident, and requires you to learn how to deal with that in specific situations (while also adding to the decision space for the other side).
I'm looking at it on MacBook with 40% brightness and I can tell the difference, but yeah it's only slightly better. Reading the comment I was expecting some orange outline but there's only a very light "gamma" difference.
You have to imagine that we're recognizing and reacting to these things faster than we're often aware of. It's largely an unconscious process where edge detection is the very first step. Even a subtle change like this will have a significant impact on how quickly you can visually process and react to it. This patch is meant to make it easier to discern the model from the background and it does that perfectly without affecting game balance too much across the game.
I have an ASUS and I switched to its "FPS" mode in Armoury Crate.I was then able to see the difference, but it is really subtle. My monitor doesn't have 4K, so maybe that might make the difference.