I don't understand how it is broken by design? 144 pages is fairly short and compact for a security tool. Think about how many endless pages are written about the security tools in Mac or Windows. sudo is a pretty broad tool and its used for a lot of enterprise control. When it comes to the casual user, usually the distro will abstract the tool to a pretty common denominator. Much like Mac and Windows abstract the complex security layers within each of their OSes for the home user.
I mean seriously, I think someone is missing the point here. That 144 page manual is for someone who is sitting in an admin chair, who will need to properly craft the file so that a central Unix/Linux box is properly maintained. I know MCSEs that have read tomes of information related to Windows security and I'm pretty sure the same holds true for Mac people as well.
This is my take on your comment, and if I'm wrong on this feel free to catch me on that. You are expecting home users to read something that is more geared for admins. Maybe even small time admins to read that, when usually the default out-of-box is good enough for a 10~50 employee setup. The question being now, "Would you expect a home user or a small time admin to be up to the same level, when it comes to security, as say an MCSE?" I don't think so and likewise, the sudo man page (and also PAM and dbus) is mostly geared for your high level admins who are going to need to know that kind of stuff.
So I don't think it is broken by design because it works as intended for the audience that it was geared for. For the home user and small business, if the default sudoers, pam.d/*, or dbus.conf isn't secure, that's mostly a problem with the distro makers and poor choice for their target audience. Not a sign that users need to read 600+ pages of manual. Overall, ask any admin of any OS how many pages it would take them to completely describe a tool like sudo for their OS and I'm pretty sure you'll find that 144 pages is on the low end of that scale.