As far as the claim system goes, it really is just fine. Sure, it could use a few tweaks (the drop PL thing being one of them), but it works otherwise. As for it messing up open-world content, I'm inclined to disagree. Even if you couldn't attack other people's claims, you could still fill a party with DDs and keep the healers in a second party, which is pretty much a zerg-fest.

As for party size, it's currently not one of the top priorities, nor should it be. This game needs to work well with 8 man groups before it will ever be great with 16, 24, or 32 man groups. As such, the Dev team is taking the right approach in making content for 8, and limiting groups to that size for the time being. The time will come for content designed for more people, but there is still a lot to do before the game gets to that point. It is unfortunate that it was so deeply flawed at launch, because the player community is ready for large-scale challenges, but the game is not.