Fair point, but my original point/issue still stands. The admin here is saying "lemmy.ml is overloaded, use other instances instead" and that advice isn't really helpful, at least in the present state of things. Right now, we have an influx of novice users coming in from Reddit, and other servers either not accepting applications at the moment, or they are tooniche/specific (or inflexible, like Beehaw); finally at the moment, majority of the content is on lemmy.ml. So the end result is that lemmy.ml is one of the main viable servers.
If people join some random server which doesn't have the content they're after, they'll either lose interest, OR they may continue to consume the content on emmy.ml via federation, but then that's not really going to solve the load issue since the content on lemmy.ml isn't distributed/replicated.
I understand your point of ever growing data and how it may be better if that data is transient and not there forever, but for a news aggregator and forum type social network like Reddit (and now Lemmy), data is everything. If that data isn't available, or not going to available in the future, or will not be visible to audiences due to it being on some random server, it's going to give content creators much incentive to create content, and no content == no users. This sort of model/thinking will be doomed to failure, or be forever relegated to niche/enthusiast status, where only niche communities will thrive on specific servers targeting that niche. Which I guess is the ultimate goal of federation where every topic/community has its own server? But to get there, you'll need interested users, and to get users to be interested you need a stable, singular place you can point them to, where they can post content knowing. And maybe, as that server grows, the admin could start splitting off the larger communities into their own individual instances?