No forum can compete or even come close to what Bitcointalk has achieved when you talk of forums about Bitcoin and Cryptocurrency, Bitcointalk is what Google and all into Bitcoin are recommending, all forums exist because of their niche, Bitcointalk and all the other forums are popular because of the popularity of Bitcointalk.
Their links and presence of other Forums here will not hurt Bitcointalk, they are not going to lose their reputation because of other forums they have built their reputation for so many years to be threatened by other forums.
And besides they have the same goal and that is promoting the adoption of Bitcoin.