On my CentOS 7 system, there is no iproute2 package, but there is an iproute package. Neither 'man iproute' nor 'man iproute2' produce any man pages. The iproute package provides the contents of /etc/iproute2, among other things, so why is the package name just iproute? The man page for ip has the name iproute2 at the very bottom, where it is easily missed. It would never have occurred to me to look for either iproute or iproute2 for information on ip had I not come across this posting. A little consistency of naming, with better cross referencing, would sure be nice...
What you're describing seems like an inexcusable state of affairs, but as a practical matter `man -k <search term>` or `apropos <search term>` is useful for finding poorly named manpages.
Of course in the specific case of "ip", both are going to return quite a haystack to search through...
