journald.conf(5) is ~2500 words and ~230 lines on a terminal 130 chars wide. Not exactly a book. systemd-journald(8) is ~220 lines and systemd(1) is ~750 lines. Big? yes. But nothing compared to some other man-pages (ever tried `man gcc` or `man bash`?)

People complain about how bad or non-existing Linux's man-pages are compared to the BSDs, and then systemd comes along with a really extensive and well-written set of manpages and people complain that it's too much

Can't make everyone happy I guess...