1 - You may see it as a huge leap, but there are plenty of N's that view your "types" version of the world as obstinate. In terms of generalities, I don't see a lot of pure creativity emerging from STJ's. It's just not their strength. That's all I will say about this for the moment.
Ah, that trap -- "My blanket statement is excusable because lots of people agree with it". I would argue that in a lot of ways, Ni types are much more obstinate than SJs. I got into a long conversation with several INFJs about how they were definitely more stubborn than SJs (because SJs will change their minds immediately when presented with good evidence to the contrary, whereas it takes even more than that to convince an INFJ), and they agreed with me entirely.
I will agree with you, though, that SJ creativity isn't usually the type of creativity that is unrelated to artistic precedent. We can still be very creative people, but usually by improving established things, instead of making new ones.
2- XSTJ: "I'm right until proven wrong". Most N's don't operate this way - especially people with a high "N" quotient.
Every single ENFP I know operates this way, for the record, regardless of their "N quotient". INFPs, too, can be the same way -- making very strong opinionated statements only to completely reverse their seemingly cemented opinion when presented with good opposing evidence.
Which is why we always try to make an "educated" guess about things that are uncertain instead of rely on proven techniques.
I don't know where the "instead of" came from, here. Those things are not mutually exclusive. I would argue that they don't even link to each other that much. SJs make educated guesses every day -- they just don't usually call them that.
To answer your question: things "get done" in an "N" world by attempting to find a "gray zone" that is optimized. The decisions that are made are open-ended conclusions, even for an ENTJ - which is why an ENTJ is good at creating order out of chaos, while an ESTJ is good at using established techniques to create stability.
I appreciate this answer -- thank you.

But I would argue that ESTJs optimize that "gray zone" in literally exactly the same way as the ENTJ, with the only difference being that the philosophical aspect is implied.
ENTJ: There is no perfect solution, so I'll use this one, because it's better than the others.
ESTJ: I'll use this one, because it's better than the others.
It's almost exactly the same thing. In fact, if you ever get an ESTJ into a philosophical debate, they will agree with you that nothing is certain. They know that as well as anyone. They just don't enjoy thinking about it, like you do. That's how I see it.
EDIT:
I don't disagree here with what you're saying here, but I think it's possible for an STJ to not subscribe to absolutes. Maybe it comes across that way, maybe it's explained that way because of poor word choice, but STJs are as good as their Si. If they don't have a depth of experiences to draw from, they are likely to subscribe to the black/white way of thinking. Otherwise, while they have a strong connection to their 'way', they are willing to consider, even try others' way and generally let them do 'them'. At least this is how I see it, as my Si has taught me that there are thousands of way to approach life, and am generally open to other approaches, as long as it's not encroaching on my values (Fi).

This is totally true.