What happened to the SGC?

[Hartzilla2007]

...We know that Pegasus stargates supersede the MW gates, so when anyone dials Earth, the Atlantis gate would activate...

Could I ask where this idea came from? I'm a bit lost.

Yes, I know that the Atlantis gate (well...ALL of Atlantis) is now on Earth, but why do you say the Pegasus gates supersede the MW ones, and why would the Atlantis gate automatically be the arrival point for anyone gating to Earth?

In Enemy at the Gate, its established that Pegasus Gates override Milky Way Gates. The Wraith bring a Pegasus gate with them which supersedes the Eath gate at the SGC. When Atlantis lands on earth, its gate would also supersede the SGC gate.

Plus even if the Pegasus gates didn't supersede Milky Way Gates, Atlantis and the Wraith Hive had DHDs and SG-1 did point out that any gate on Earth with a DHD automaticaly supersede the SGC gate wich doesn't have a DHD.