This is said so confidently, but clearly with little to no experience with the military or the VA to back it up. No vet is receiving benefits without something to back up their disability rating, even if that rating is higher than it seemingly "should" be. Some disabilities are easier to establish than others, because the issue causing the disability is so prevalent in the service that the military has little basis to deny them. Hearing loss is a common one. That said, I'm a vet, with significant hearing loss due to my time in (I was an F-16 maintainer on the flightline, an extremely intense noise environment). I'm not eligible for _any_ disability rating at all, because I did not report issues while I was still in the service; but hearing loss issues often take time to become apparent, and it's not like we were being tested for it. It was not uncommon for someone to forget their earplugs (the second layer of hearing protection we had, under our headset), and be essentially forced to go out on the flightline anyway to handle some task around running engines. These events would be downplayed, but just one instance of that can cause irreversible hearing loss.
But that's just a specific issue relevant to my time in the service. The bottom line is that unless you report every little thing that _might_ cause an issue later, you're going to be up shit creek when you get out and find out that something you were exposed to during your service is causing an expensive medical issue that you have to deal with. There are all kinds of fucked up things people had to do while they were in, that they struggle to get compensation for now that the consequences are catching up, because the issues aren't straightforwardly attributable to some event during your service, like with combat injuries. Burn pits are the most notorious one - you have advocates like Jon Stewart fighting in Congress to pass laws to support vets who were forced to work those pits and are now battling all kinds of complications. If anyone should be an obvious beneficiary of the disability system, beyond those with combat injuries, it should be those folks - but they are largely left hanging in the wind. In the case of burn pits especially, the military _knew_ there were consequences to having soldiers work them, but chalked it up as the cost of war.
Frankly, from what I've observed, once vets are out of the service, our country largely gives them the middle finger when they struggle with mental or physical health issues. I say "them" here, because I'm not a combat veteran, and I'm lucky that I had it pretty easy during my tenure (2009-2015), but for many, that is very much not the case. Yeah, nobody in Congress is going to stand up in front of everyone and say "let's make disability benefits harder to obtain" - but I have no doubt they'd have few, if any, qualms about doing it behind closed doors.