Long story short:
1) To stop some logs, it is enough to add a new empty file called DISABLE_CORE_DUMP in the /mnt/us/ (visible root via USB). Heavy core dumps won't show up anymore. Only ones that show up are Indexer Dumps (a few tens of KBs) every now and then. Context: I also have blocked all logging, and indexer dumps says something like "this is a diff between files on device and cc.db" - I am pretty sure this is because there is a mismatch between cloud (which never sees any logs from my Kindle Scribe) and local files
2) To hard stop EVERYTHING, block /usr/bin/dump-stack . This will prevent ALL logs. Side effect: usbnet session is very laggy in between actions. Most probably because Kindle still tries to run dump-stack, but encounters wrong exit statuses.
In the end, I rolled back to 5.16.2.0.1 and plan to stay here for a long time.
hf versions seem to be much more chatty in terms of dumps and stuff.
P.S. Also, I just figured I have been missing out on this little gem of a GitHub page
and it works only on non-hf kindle due to browser support.
https://github.com/KindleModding/KWebBrew