Probably a very polarizing question.
On the one hand, having most of the users and communities on LW causes technical issues (see this post), and also gives the LW staff too much power over Lemmy as a whole.
On the other hand, with 18k MAU on LW out of 47k (https://fedidb.org/software/lemmy/), every community listed there has a much higher chance of visibility compared to an alternative hosted on another instance
Communities on big instances have a chance to grow. So once it gets big enough on something like world, they could put up a movement post and switch the community onto a smaller server. I have a lemmy ml community but it only has 227 subs so its currently not worth moving. There are enough subscribers that some posts get upvoted and end up like with 25 upvotes in a hurry so they appear on the tops lists. Obviously, the more the community hits the top lists, the more people will see it and maybe subscribe to it.
I would have thought that a smaller community would be easier to move, as there would be less inertia and inconvenience. I’ve deliberately created some communities on smaller servers and cross-posted to more general communities on larger servers to help with visibilty.