Hello Disctanger.
Have you measured the speeds that you get with OEM's officially supplied software, if the OEM supplies any?
It been my experience that some 'open source' OEM's quote the theoretical maximum specs if hardware and software were optimized.
Some OEM's provide very limited support for their 'open source' boards, and rely on the community to optimize the software and even the hardware.
If this is one of those OEM's, then it's up to the community (people like you) to optimize the software (or even the hardware).
You can search these forums to see if anyone has found solutions, and sometimes someone might answer with a suggestion or a solution.
The Armbian build system is an ideal platform for you to develop solutions, providing an easy way to apply patches and stream improvements into the build via Github pull requests.
I took a look at your logs, and I didn't spot anything obvious. Perhaps someone more familiar with your board will turn up.
Good luck
