lemmy.world experienced explosive growth and the servers were either quite slow or were experiencing persistent 502 errors. Switching to a smaller instance the experience has been a lot more performant.
Having different accounts for different interests suggest to me that there's a missing feature in Lemmy. I can see why some people might want that, but Reddit had multisubs for that need. Lemmy doesn't have that.
Yes some kind of multi community support would be good. However, I think for more 'sensitive' content it may be inevitable to see content from widely defederarated instances.