Ok, while i agree with you there coverage is a little too broad, it appears we are arguing in Circles. I am going to say my two cents, and then recommend this thread for closing.
Take a look as
MW:CVBased on MarioWiki:Canonicity, there is no "canon" regarding the Mario franchise. Since there is no canon, we cover any Mario relate media product given some sort of official authorization by Nintendo at some point in time, be it through the Official Nintendo Seal or a contract with another company, etc. All content from such sources is allowed on this wiki, without speculating on what content from what source is more officia than other content from other sources. As Nintendo has never established an official canon regarding the Mario series, we cannot say newer or older Nintendo games, media, content, policies, etc. are more official than the others. They are all essentially as official as each other.
It states that the wiki chooses to cover Mario-related Anything from the original
Donkey Kong to
Super Mario Galaxy 2. Now, Banjo maybe stretching it a little (since he is the main character of
Banjo-Kazooie -> which is a spin off of
Diddy Kong Racing -> which is a side game of
Donkey Kong Country -> which helped
Donkey Kong establish his own franchise separate from Mario.
), but still, the important part of this is that the wiki chooses to cover it. NIWA has taken the position that if the wiki chooses to cover it, then let them, so long as a current member doesn't already cover it. Just the same, a new member can't join, unless a wiki with a similar coverage policy lets them.
Since NIWA accepted DK Wiki as a member, the DK Wiki had to have permission from Super Mario Wiki to Join. And it did. Do you honestly expect NIWA to turn around and say "Sorry, we have to kick you out. We have Mario Wiki".
Just the same, do you thing NIWA will tell Super Mario Wiki, one of the founding wikis by the way, "Sorry, but we need you to remove all DK stuff because we now have DK Wiki".
No, I don't think so. Why? because there is something more important than coverage at the core of these decisions: The principle of Choice.
It is that principle that the alliance was founded under, and the principle that has guided the alliance ever since.
Every wiki that comes to us, has chosen to be a member; just as niwa has chosen to include each and every wiki so far.