Lol the reading part.We are American. Native speakers all my life, and unlike most here, it's the only language I speak. I got all 9's though. She got three 9's and one 8.
Edit: I should say, I didn't just show up at IELTS unprepared. I prepared for 2 months with various IELTS books and online audio. I wrote exactly the way the IELTS wants you to write. Beginning paragraph, paragraphs to support, conclusion, etc. I learned how they want you to write and I wrote that way.
I studied lists of speaking topics that were asked most recently from online blogs that cover IELTS so I could have an idea in my head of my general answer, that way I would have more time to write notes about points I wanted to talk about extemporaneously.
The listening and reading were easiest, as a native speaker. However, all my prep work had audio that was wayyyyyyyyyyyy slower. I was shocked when the audio was about twice as fast as what I prepared with, but I had no issues understanding.
Reading was super easy. I finished and went to the bathroom with someone who accompanied me, and came back and still sat around doing nothing staring at the clock.
I found speaking and reading the easiest and am not a native speaker. I kind of understood you are natives because of your scores, but even for the natives, it is a struggle to score 9 in writing. Your preparation explains it.
All the best