@creative_writer big question! Might depend on who you ask ay, but I am pretty sure the whole reason that the diagnosis of 'PTSD' was developed was as an alternative to the pathologising that was going on prior. Personally I prefer to describe it as a 'psychological injury' as opposed to a disorder for the same reason.
I think if we make a comparison to a physical injury, it might help us understand why some people develop ongoing symptoms of distress, and others don't, even if they were exposed to similarly traumatising events.
Let's say you got two people who both got hit with a similar event - one person has come away with a sprain, the other with a broken leg. Maybe that's cos already, person A had privilege growing up, so they had better access to nutritional food growing up and their bones are stronger.
Then, we also see that Person A has good medical care, so in the immediate aftermath of the injury, their leg is already in a splint. Person B's broken leg doesn't get wound dressings for aaaages.
Turns out Person B's family is also not particularly supportive, so they don't even have anyone popping around to check on them or do stuff around the house. So Person B has to do it alone, which means constantly putting weight on their leg, making it heal even slower.
So even though Persons A and B both had exposure to a similar trauma, one of them is all healed up and the other is still hobbling along months or years later. Would we say that Person B is 'disordered' for not being able to run after all that? Heck no!
So same goes for someone who went through a traumatic psychological event, who gets little-to-no support in the immediate aftermath, who doesn't get supported by friends/family to heal properly during their initial recovery - is it any wonder they're more likely to end up with PTSD than someone with privilege, support, and access to proper care?
So to my mind, PTSD is indeed a normal reaction. In fact I could go on to argue that ALL pathology is actually just normal reactions for brains under stress but that's a ramble for another day haha