The impression I got from reading the v6 kernel code in the Lions book was that signal handling had been added in as a solution to a few specific problems (like

The impression I got from reading the v6 kernel code in the Lions book was that signal handling had been added in as a solution to a few specific problems (like "we're going to kill this process but maybe it should get a chance to clean up first"). If you're thinking about them from that viewpoint then the (now) well-known problems like interruption-of-syscalls and the initial "when you take a signal the handler gets unregistered" don't seem like such a big deal -- after all, the process is going to exit anyway.