It doesn't matter how many realms are involved. Look the system is designed in such a way that it pulls as many players from as many realms as it takes to get zones to an appropriate population level whether it is 2 realms or 20 realms. Again zones were designed with a certain population in mind. People in your mmo is intended. Competition is intended. If Blizzard wanted everyone to have competition free empty zones they would have just given us our own personal copy of whatever zone we are in.
Also please do keep in mind that cross realm zones technology also makes it possible to split overcrowded zones into separate instances so for all you know DMF island could be significantly more crowded without it.
---------- Post added 2013-06-02 at 01:14 PM ----------
Again people in your mmo are intended. I have come to the conclusion that the people still claiming they are having problems with cross realm zones are either lying through their teeth or just simply not understanding how the technology works. The sheer lack of specific information in how exactly it is causing problems just makes it more obvious that it isn't a valid complaint.