If you’re talking about communities existing on each instance, ie lemmy.world/c/photography and lemmy.ml/c/photography then yeah, those won’t sync. But the users need to coalesce around once of those, say the lemmy.ml one, then when you go to lemmy.world/c/[email protected]. The duplicate communities is no different than Reddit having 2 similar subreddits.
If you’re talking about communities existing on each instance, ie lemmy.world/c/photography and lemmy.ml/c/photography then yeah, those won’t sync. But the users need to coalesce around once of those, say the lemmy.ml one, then when you go to lemmy.world/c/[email protected]. The duplicate communities is no different than Reddit having 2 similar subreddits.