Let's clarify some things.
I never thought my device could send data without wifi turned on, that's why I've been using it offline for some months. Your procedure was absolutely coherent and answered the question. Indeed there is no need to modify the database to protect one's privacy on a kobo reader. Creating an account with a false email and then turning wifi off to perform any other operation offline is enough. Yes this is true, thank you pointing that and this definitely should be documented on a potential wiki page for new users who want to protect their privacy.
Kobo acts differently than Google, Amazon and Apple. You made me aware of that and it is also true and verified, as
this topic explains. Your contributions were truly useful and I did read all of them entirely.
Well they still gather data and they do share it, that's enough for me not to trust them and be cautious.
I chose to modify the database mainly because I do want to use wifi and I don't want to sign the EULA for ethical reasons. This latest statement should be enough so I don't have to justify my choices further. There are other minor reasons why I chose it that I already explained and I'm tired to repeat it again and again.
Yes the web browser is not secure and it would be incoherent to use it. As I explained there are third party apps that use wifi for interesting functionality and I want to be able to use them without worrying for my privacy. Planning to use ssh over wifi is enough to justify my choice anyway. I will also probably run some experiments on the eink display. So I will tweak the hosts file and any other needed file as I need. My device, my logic, my choices.