Hopefully it always stays that way. But that sort of tends to be a "it's ok until it isn't" sort of situation. I had always raised my puppies the way I did my Parvo litter. Had raised my other litter they same way. And yea, all puppies did fine...until they didn't. It's like that with a lot of stuff I suppose.
Most often what happens with puppies is that they get Parvo before the vaccine has a chance to take effect, so their body ends up battling both the actual virus and the vaccine at the same time. And as such, it can be harder to treat, although I definitely wouldn't say that "most vaccinated puppies who get Parvo will die". FWIW One of my dogs got Kennel Cough a couple days after getting her Rabies vaccine and became deathly ill from the KC.
Much of if a puppy can survive parvo depends on how quickly the puppy's symptoms develop, how quickly they begin treatment, how dedicated their owner and vet are to saving them and what else is going on with them. It's not just badly timed vaccines that can increase the risk of death from parvo. Puppies who get parvo while battling intestinal parasites are at increased risk of dying. As are puppies who have anything else going on that affects their immune systems - demodex, coccidia, giardia, kennel cough, etc. beyodn that many Parvo puppies, both vaccinated and not die because treatment is not given quickly or seriously enough. Symptoms can turn from seemingly minor to life threatening in the same day. Vets sometimes don't think Parvo if the classic symptoms aren't there (namely bloody diarrhea). Or their owners can't afford treatment. Or their vet tells them it's likely the puppy will die anyway. Or they feel they can give herbal remedies and Pedialyte and the puppy will be ok. There's really a lot of variables that come into play.
And yes, breed and individual dog can play a part in the effectiveness of vaccines too. It seems to be harder to form immunity from vaccines in certain breeds (APBT, Rotties, Dobes) than in others. And certain individuals regardless of breed can't form immunity from vaccines, no matter how many they get. So that can undoubtedly add in on the vaccinated dogs getting Parvo.
The nature of Parvo is that it is causes short but intense symptoms which can be life threatening in young puppies. You often know within 24-72 hours of them developing symptoms if they are going to make it or not. It is a danger mostly to young puppies because it attacks the rapidly dividing cells of their intestines. Adult dogs generally have a much hardier intestinal tract, so they tend to be at much less risk for Parvo even when directly exposed. None of my adult dogs had any symptoms and none had a "current" (given that year) Parvo vaccine. The 14 week old puppy I had at the time, who was fully vaccinated also did not get any symptoms.
Well, it's not really as simple as that. Dogs who are hardwired to be gregarious and not overly sensitive to their environments
can often be fine without much socialization. I have known dogs who were taken from bad situations past the age of prime socialization and they've been fine. And I've known dogs taken from similar situations who aren't. Some of it depends on the individual circumstance and dog for sure (two littermates raised with little human contact may act completely different) and socialization is certainly ideal and certainly what I would encourage everyone to do. But not every dog who didn't receive tons and tons and tons of socialization is going to live their life in fear and misery. The Irish Setter we had when I was a kid had little socialization away from home but he was always a pretty happy, friendly, doofy dog. My first dog though, no way he could have become the good dog he did without extensive, ongoing socialization and training.
The breeds I have had for half my life or so now, I would never encourage one to risk not socializing extensively. While I've known some who were ok with less socialization, I wouldn't feel comfortable raising one that way. Breeds that are hard wired to be guardy or suspicious or standoffish with people and super alert to their surroundings definitely should have plenty of proper early socialization and training. It doesn't matter to me though, even if I had a super friendly breed or puppy, I'd still do all the early socialization and training because that's what I think the best way to raise the sort of dog I want is
Luckily enough, the Parvo vaccine is actually pretty effective. Some vaccines aren't (Lepto, Lyme, Bordatella) though.