Ok, found what the problem was. Lightdm was not starting with 96 dpi. Also the settings in
fonts.conf are simply ignored.
To solve this, had to create the
[[ -f ~/.Xresources ]] && xrdb -merge -I$HOME ~/.Xresources
With this, and after restarting the lightdm service, i3 was finally set to 96 dpi and font antialias and hinting is now working as expected.
I am not sure how lightdm manages these resources, since it works fine for DEs like Xfce. I know nothing of how display managers work. But I won’t be learning this time either. My plan is to remove it (along with Xfce) once i3 is fully set on my machine and I am comfortable enough to leave behind 2 decades of point-and-click DEs.
Anyways, all good now. Cheers and thanks.