The 8w9 that I'm closest with had never any problems asserting himself. From his birth he strongly asserted his independence and pushed against anyone who attempted to control him. This mostly being his parents, for obvious reasons. Extremely aware of 'the stupid people' in his life (blaming others, not himself).
The 9w8 on the other hand grew up shy and over-attached to the people in his life, never had a bad word to say about anyone (it was a problem). It took him a long time to become assertive, well into adulthood. Nowadays he's a powerful person, exuding receptive autonomy and strength, but he's also about 50 years old and had to grow into this.
Neither of them are very talkative, but the 8w9 is extremely aggressive in regards to the world. Not angry (outwardly at least), but aggressive. Meaning that he -always- needs to take control of his circumstances and he easily challenges people, to see what they're made of and if they can stand their ground. He has the assumption that most can't. He's right. The 9w8 on the other hand, while he's a super hard worker and has a ton of energy, he gets stuck in the same place for decades. It's too easy for him to forget his own priorities. And as I said, he think the best of others first.
So, to sum it up;
Essentially, the 8w9 is an 8 first, with all of the type's difficulties. Hyper-awareness of people's vulnerabilities, thinking of others as weak-willed and spineless as a result (blindness to their positive qualities). Negative worldview. Excessive energy leading to domineering his environment from a very young age. Aggressive about their autonomy. Black and white worldview.
The 9w8 is a 9 first, and has issues with over-dependence, weak boundaries (especially when younger), sees the positive in people (blindness to their negative qualities), lose sight of own priorities. Extremely receptive. Shades of grey worldview.
Both of them are stubborn as all hell, quiet, need their independence. Curiously enough, neither of them can stand arguing.