Drop Alliance Quest Battlegroup Joining Criteria
Many groups of mixed ability must have the same problem, but slow joining makes it hard to make good progress, and weaker players cannot be made to join the later quests. About the only way to offset this is for stronger players to join the later quests and make them more attractive, but this is hard if the quests won't open up, as they're busy piling into the first battlegroup.
There's no need for the game to shepherd players first into battlegroup 1 then group 2: they'll do that anyway. But the restriction upon being able to join later groups makes it hard on those of us who are attempting to push the envelope and stretch the alliance when it isn't yet ready for the next map.
Allowing groups to spread out sooner into later groups makes for a better game dynamic, so the requirement to have a minimum membership taking part in the the previous group should be dropped.