Thanks for the sharing. I suspect simply boot from a Linux LiveCD (e.g. GParted) should able to completely remove the APFS partition and re-format the SSD / HDD according.
I did think about go back to Sierra, I don't mind spend few hours to do that. However, my 1080Ti works so well in High Sierra, and I don't want to go back to an older OS that the driver may be not that perfect. Also, there were some other bugs happened on my cMP in Sierra Apple never fixed (I did submit the bug report, and work with them, but just no fix yet). That's the main reason why I upgrade to High Sierra once it available.
At this moment, disable TRIM alleviate the problem. So, I will stay at High Sierra. But I may go back to HFS+, in order to allow me to use bootcamp manager in Windows to boot back to MacOS.