it is avoidable (or at least it can be slowed down enough to be manageable) if there is a pre-existing culture. lemmy simply didn’t have one beyond a vague foss/privacy focus and whatever’s going on over at lemmygrad, so the reddit migration brought over a lot of people who then set it up to be exactly like what they were used to (being reddit).
if you go look at mastodon (or the microblogging fedi in general) for example, the biggest instances still have their fair share of “twitteriness”, but as you get to the smaller, tigher knit, and stricter moderated instances, you’ll see a culture that’s significantly more laid back (and yes, very gay).
i think what’s happening is that the big instances act as a “firewall” of sorts. catching the people who just want a twitter 2. and the people who want more and vibe with the smaller fedi culture will then self-select and migrate out into the smaller instances after realizing all the cool people (and in lemmy’s case, communities) they follow are on those smaller instances and all the interaction they get on the large instances are boring reply guys (or worse, actual bigots that go unmoderated because no large instance can keep up with moderation and .world has inadvertently doomed itself even if it has not realized it yet)
over time i expect lemmy to have it’s own share of these tight knit instances - and as the hype dies down and the trolls start getting bored, communities start migrating, moderation tools improve, and yes - the occasional defederations that will inevitably happen - .world and it’s ilk will be the reddit 2 some people want to have (with the good and the bad), while a different, unique, culture will slowly but surely form across instances that intentionally keep themselves smaller and more focused. and of course you’d be able to talk across communities in these separate “sides” of the threadiverse thanks to federation.