Rainbow Basilisk dead? Yes, we're that awesome.

[Redbert]

A level 30 dungeon will be included as well. That should make the grind to 50 more engaging.

You don't even know what all is going to be in this dungeon. It is possible there will be no exp gain, or a small amount.
Also, the dungeons may have a cooldown of a few hours to a day, making them impractical to gain exp with.