This is a Frame Challenge
Our modern understanding of the effects of war on the individual soldier has, in my opinion, led us to erroneously believe that war today is somehow worse than it was in yesteryear. And that has led you to believe that it can be made ever so much worse, leading to asking just how much psychological damage can be fixed. You've included a description of weaponry that's designed to, theoretically, maximize psychological stress and you have created a condition (not hitting population centers) to maximize the separation between soldier and civilian.
It's an entirely false premise.
War is individually more brutal the further back you go in history
Modern warfare is certainly more instantaneously destructive than wars in the past. But destructiveness alone doesn't create deeper scars on the individual soldier. The U.S. Civil War meets all of your criteria and yet I'd bet you think it's "less violent" than wars today or in your near future. Some states had to devote a third (a third!) of their annual budget to prosthetic limbs. Some towns lost all of their military-age men. Photographs of the battles are sickening and depict, in my opinion, as much or more violence as you're trying to consider.
And it gets worse the further back you go. People a thousand years ago waded through blood, too often had to kill face-to-face, and had the pleasure of seeing bodies trampled by horses and chariots. Theirs was a day when all too often it took a long time to die.
I believe it's false to believe that war today is more onerous than it was in the past. I believe it was, for the individual soldier, much more onerous in the past. Humanity simply didn't have the psychology skills to understand the problem. If you have any technology at all in your near future, that technology will be used to strike from a distance and remove the expensive-to-train and expensive-to-fix soldier from the field.
Not surprisingly, "statistically" it appears that there was less cancer 200 years ago than today. That premise is false, too. People 200 years ago simply didn't understand cancer as well as we do today and so its consequences were recorded as something else, skewing the historical data. I believe you're affected by the same problem with the psychology of war.
No modern war would ignore population centers
Humanity has long since left behind the idea that civilians are not part of the military machine—that they should be left alone or protected because they're not a threat. They are, in fact, the greatest threat. Civilians make the bullets and the bandages. Civilians make policy. Civilians make war. Humanity learned a long time ago that if you want to win a war, you need to beat the capacity for war out of the civilian population.
To make a point, nuclear weapons don't exist to fight armies. They exist to destroy population centers. Oh, we may try to be more surgical than in years past with so-called smart weapons that target and destroy specific factories, power generation plants and dams, government centers... but you're still attacking civilians.
I'm not going to ask, but it wouldn't surprise me that you (like I) are a U.S. citizen. It's been 150 years since we experienced a war on our own soil—excluding the BLM riots, Capitol incursion, gangs, school bombings, and serial killers. I'm not being facetious, those are terrible things, but they're not a real war because they can't bring the "big guns" to bear. We Americans have a bit of a skewed idea about the tragedy of war because it's been a very, very long time since we experienced it first-hand. Unlike a great many other nations on our fair planet that have experienced it first hand and whose citizens likely have a very specific opinion about our average citizen's ability to know what real war is.
Psychology is part of all wars, but it's not the driving purpose of any war
No war would be fought for the purpose of hurting the surviving soldiers in a way that makes their continued presence in society a problem. Some wars are fought to humiliate the enemy. Some wars are fought to capture a resource. Some wars are fought to promote religion. Some wars are fought to "finalize a divorce." No war is fought to intentionally keep the enemy alive but in mental pain.
I once had a discussion with a friend in the Finnish military. He made an interesting point. As part of his training, he was taught that, when possible, shoot to wound-and-disable, not to kill. The goal was two-fold: (a) to stop the other guy from shooting at you and (b) to force one or two other people to be engaged getting the wounded soldier off the field. The goal wasn't to cause the target soldier mental trauma. To quote U.S. Civil War general Tecumseh Sherman, "all war is hell." The goal was to cause as many people to stop shooting bullets as possible.
But that's also a reflection of modern efforts to "civilize" warfare. During WWI we used gas and machine guns. During the US/USSR Cold War it was nuclear weapons. Today we worry about the use of biological weapons (to the point of a great many people thinking COVID-19 was a biological weapon run amok). Despite efforts to "civilize" war, I suspect that when you're in the proverbial trenches, the goal is reflected in a statement by U.S. general George Patton, “No dumb bastard ever won a war by going out and dying for his country. He won it by making some other dumb bastard die for his country.”
But the central problem is that your question is the proverbial blind being led by the blind
But here's the biggest problem: you don't know what you're doing. Unlike authors like Arthur C. Clark and Larry Niven who had advanced degrees before they wrote their works, you don't have an advanced degree in psychology (or you wouldn't be asking this question here). And you're asking people who don't have advanced degrees in psychology what the upper limit is—if there's any factual reduction in PTSD and other psychological trauma at all. The veterans I've spoken to all explain that the therapy/medicine helps them cope. It doesn't solve anything, because the memories remain and the cultural conditioning that makes those memories unacceptable/traumatic also remains.
Unless you think that removing said conditioning or removing memories is a legitimate answer to your question. Oh, the consequences that technology would have on society! It's also been explored by SciFi before.
Frankly, the only user I can think of who could possibly answer this question with authority is @Otkin, who hasn't posted a question or answer on the Stack since last March.