I am thinking why the default user of Debian 8.x is not in sudoers list although it has su/root/... access which is not safer than sudo here
Using sudo is better (safer) than opening a session as root for a number of reasons, including ...
I try to stick to defaults in my Debian use. Therefore, I have not added my default user in sudoer list.
However, it has those shortcomings above.
Still, I am thinking if I should change the default way.