when the number of staff increases, we make the number of posts bigger, which makes it harder,

Number of posts shouldn't decide who's mod or admin or supermod or whatever other rank gives power.

then what should if not the activeness of the user?

first off,
i dont think requiring a fixed number of posts is a good idea as a requirement for staff application
requiring x number of posts gives people an aim to reach, which is not that closely related to what being a good mod or admin really is.

no more mod s or super mods.

well dont take it TOO LITERALLY
activeness as in posting whatever is not a good basis for making someone a staff member
activeness without spamming (Stupid Pointless Annoying Messages) and also being a good judge in situations and affairs of any particular site, is NOT the one starting stupidity, fights and spams in thread, and most importantly, HELPS people, not just about finding mugen stuff, but helping about everything

like if a random dude makes a site, so if his trusted friend just posted like 10 times but regulates the site everyday, sees to it that rules are enforced, logging in everyday, is that guy not a good potential mod/admin? thats still a lot better staff than someone who spams the hell out of a site. contributing and spamming/trying to reach as many posts as he/she can are 2 different things.

i already made a "sign", should i post the vid 'bout it here? turning it into a gif, will take away all my powers sad