[Leokaiser]

Regardless of what was 'classic' behavior back in the day, players here are generally able to deal with much larger areas than what might have been the norm when you last played, due to having better knowledge, mechanics and gear. In light of this, there really isn't 'plenty to go around' if you try to divide that area up.

As Ambrotos says, it might not be against the rules, but it is very poor form to come in and claim a significant number of mobs an existing group was already pulling. It does suck to arrive in a zone to find there is no (or very limited) space for you, but sucking it up and moving somewhere else is the right thing to do.