I wouldn't try to justify the awfully huge number of commands that many unix util implementations have - which seems like an anti-unix design movement to me - but you can at least cut down the 30 minutes of man page spelunking with man <foo> | grep -A 3 "\<flag>". Adjust -A argument as needed.

(for example, if you don't know what -A does on grep, run `man grep | grep -A 3 "\-A"`).

You can also use / in man to do a search in man. (Assuming your pager supports it, don't forget to use the home key to go back to the beginning for a new search option.)

> have you ever tried to discern a gcc command with 12 compilation flags enabled?

This isn't a 'discoverability' problem - the problem is the complex task. Most of what you're doing on the commandline isn't "gcc with 12 compilation flags". "How do I print this document?" is an example of poor discoverability on the CLI; command flags are not.

To print, one used to pipe things into the lpr command, discoverable using the apropos command.

    $ apropros print
    bash: apropros: command not found
    $ man print | head -n 1
    RUN-MAILCAP(1)               Run Mailcap    Programs               RUN-MAILCAP(1)
    $ man -k print | wc -l     # lp/lpr is in this list... but you have to find them in a list of 200.
    196
    $ man printer
    No manual entry for printer

It's not great discoverability. 'man -k printer' is the best I found so far to find lpr, but it took a few goes to find it.

Here's zsh on my machine: http://imgur.com/dZshfUR

This switch lacks documentation