Yes you're negative. You have stated that the possibility of a "crappy" solution is within the range of your expectation as regards the game and Muse's capabilities. That sounds pretty insulting, given the great game that the development team have already produced and continue to develop. If your expectations are so low, why are you here?
Personally, my range of expectations from Muse for Adventure Mode ranges from "Fantastic!" to "Awesome!"
I have no idea how PSO handles this type of mechanic, but based on what I'm familiar with a GW type system of handling inter-town travel and instanced PvE encounters would be a practical way of addressing the issue. It's also adaptable to a limited vs. fully explorable town simulation. Whatever system is developed will have to cope with the situation where players are in the wrong place in relation to their online crew/team mates.
Negative and positive =/= negative. Balance = Neutral. I try to keep realistic expectations so I don't get disappointed, but I'm invested in seeing how things turn out, I paid for the game after all I would like to see where it goes.
That aside, PSO generally had players starting in a sort of hub town (based on where they were in the story) with all the bits one might need. Stores, trading, and more importantly other players. It was an area for social interaction and "maintenance" of a sort in selling junk, upgrading gear, so on etc (They also had housing with a good bit of customization AND functions, but I'm not expecting that here).
Players would group up and select an instance of the world they wished to enter (unlocked via story progression and replayable for side missions) after which they would be teleported to a linear set of "rooms" which comprised each level and would lead to the next. At any time one could leave for the hub, and come back at the start of the section they began.
As I recall anyhow, It's been a while and while it may not sound like much due to the level design and world building it usually resulted in a fun and entertaining experience with relatively low server requirements.
Gw (original) Could work I suppose, and the concept is quite similar. In both, you will not encounter players outside your group in the outside "world" unless an event calls for it. Rather than a persistent open world, it is a series of instances. But done well it can provide a good experience with less server load and necessary programming.