Welcome to Brisgard. Most of the large guilds enter alliance specifically to block the rest of the guilds and they benefit immensely by mechanically trading the sectors back and forth while the blocked guilds can only watch. You’re right, it isn’t easy but they do it every time just the same because they’re used to it. And crossworld would make communication so much harder it would definitely stop it.
Then stop it in Bisgard. Or leave Bisgard. There are options beside ruining the game for the rest of us.
Here's a possible solution. Have the other guilds pick one to defeat. You have 9 days to organize or even pre-organize. Start rallying now for the sessions that may happen weeks from now. All of you that got blocked this session should organize. Then each of the leaders reach out to guilds of similar size. Then when/if you come together again. Pick one guild and hit them hard.
I don't suspect it will be easy but, in time, you all will have a list of offending guilds. Circulate that list, remind each other. Get a group thread going, Discuss among your selves.
We've been blocked too but it's like plundering. Sure it's really bad one or two sessions but you get your opportunities.