I don't know that I agree that innate temperament is so so much more noticeable/important than environmental socialization. I think they are both important. Granted, when I see a well behaved, friendly dog or pup, my mind doesn't tend to jump to socialization OR genetics. Rather, I tend to think about the behavioral "symptoms" that are staring me in the face (i.e "wow he's so friendly" or "that's a pretty aloof little dog" or "that puppy is skittish!") rather than the cause. I've fostered dogs and puppies, been involved in rescue on and off for years, and had a handful of my own (family) dogs through the years. Each and every dog/pup had his or her own distinct personality and temperament, some have been 'softer,' some more naturally gregarious, some 'harder' temperaments, some naturally wary and aloof of new sights and sounds. I've had the puppy that flipped over on her back and peed whenever you approached her standing up to the puppy that thought it wise to growl and bark and try to chase a horse the first time she saw one.
That said, despite the innate temperamental differences, socialization ABSOLUTELY plays a role. Is there a difference (on average) between the dog whose owner took it out to meet 100 new people and 100 new places before it turned 12 weeks and the puppy who just lived its life alongside the family without socialization time specifically set aside? Maybe, maybe not. But is there a difference between the dogs who lived in a garage for the first 5 months of their life with zero human interaction and those who grew up in a social atmosphere? In my experience, that's a yes to the vast majority of cases. The bolder dogs tend to come around quicker than the softer, more skittish ones, but when the world is entirely new to you, it doesn't matter if you're innately happy-go-lucky or innately a little more reserved... at first, everything is scary.
Do I think Boo was well socialized as a puppy? No, probably not in the way that we talk about it on this board. She shied away from storm drains for the first year that we had her and was scared of the dishwasher opening and closing. Might a bolder dog have taken these little things in stride? Maybe. But even a soft dog who has been exposed to these things (discounting people and other living things to a degree) as a young dog doesn't tend to react shyly to those things that they were regularly exposed to (I put "things" and "people" in different categories, because living things are sporadic and unpredictable, unlike an inanimate object and tend to produce fear reactions for a longer period of time than things that remain constant). That said, I'm also fairly certain that Boo wasn't living alone in a crate for her first three years, because her reaction to most everyday things (wood floors, lights going on and off, the doorbell, the telephone, stream water, concrete, carpet, dog bowls, doorways, etc) were all pretty nonchalant.
That was a pretty long response to a fairly straightforward question, but I guess I just hate to jump to one side of the "nature" or "nurture" debate when there are so so many factors and I think that both play a role. Socialization doesn't have to be in the form of specified daily socialization activities. Socialization to me is just a process of observing and participating in the world so that one becomes accustomed to its happenings. And yes, every TRULY unsocialized dog that I've ever met (solid innate temperament or not) has not had the opportunity to express that friendly innate temperament to the best of its ability, as it might have had it grown up experiencing the world.
I don't think on an average walk down the street that I could tell you which dogs grew up in an average home, versus those who underwent intensive socialization activities. But yes, I don't doubt that I could pick out which dog at a shelter was raised in a home alongside people versus which grew up in the shelter with zero human interaction apart from feeding time. All this regardless of their innate temperament.
As a sidenote - I feel it imperative to mention that I'm talking exclusively about domestic dogs. I've never worked with wolfdogs, coydogs, or any other hybrid and so don't have any opinion on the interaction of socialization and genetics on the behavior of these animals, although I'd imagine it to be very different from an average dog.
I also feel it imperative to mention that "aloof," "friendly," "independent," "cautious," etc. are all good temperamental descriptions that may or may not be influenced by socialization. You're not going to turn an aloof dog into a social butterfly via socialization. That said, I don't think of an aloof dog as a scared dog. I think of it as one that really couldn't give a s*** about most new people. In my mind, there is a HUGE difference between aloof/cautious and unsocialized. And honestly, some of the most socialized dogs that I've met are also some of the least interested in interacting with EVERY SINGLE person that they meet... because after all - if you've met millions of new people, what's one more, really? Just another day really...