This is a nice and pleasant fantasy, but in my personal experience, people who have been traumatized and deal with PTSD don't recover so easily.
Touma's having a pretty great time all round, his hot childhood friend is a little worn out but she's still super cute and cleans up real nice, and she's always super nice, thoughtful, attentive and kind to him when they're together and so grateful to have him around all the time. Maybe she has some nightmares and needs a hug once in a while (though not very often), but that just lets Touma feel like a hero when he takes care of her and she repays him in kind immediately. She's also super proactive in "getting better" and "putting herself back together", so I guess we can expect that by the end of the manga she'll be a fully functional adult with no problems whatsoever and heading towards an idyllic future.
Based on my personal experiences, what's different in reality is that the PTSD manifests way way more often, and in many more ways. Nightmares and panic attacks occur on a regular basis, maybe several times a week. Often in the middle of the night, and it can take hours to calm down. The person in question becomes distrustful of everyone, they won't just selectively completely trust one person and act super nice and rational with that person all the time like Kyouko does. Touma doesn't have to have endless discussions to convince relieve Kyouko of some paranoid delusion that he's somehow betrayed her on a regular basis. She's not being paranoid about all of Touma's friends and family secretly hating or looking down on her, and constantly shit-talking them in front of him. I wonder if he'd find her quite so attractive if that was the case. Not saying that has to be the case with every victim of PTSD, but point is that Touma has to sacrifice basically nothing and just gets a cute big-boobed GF who loves him more than anything in the world with essentially no effort, and dating someone who's been traumatized is not like that AT ALL.