Lemmy is heavier on the cpu than for example mastodon or matrix are but a lot less on the harddrive. Its insane. I use matrix the most, then lemmy, then mastodon. Still, mastodon sucks hdd like crazy, matrix as well. Only lemmy is easy on the hdd.
Of course I‘m running private instances. You can never know why public instances go bonkers. Maybe someone is abusing it for other things.
Anyway, lemmy does have some moderation tools but I agree. They need work. You have to know a lot about linux, databases and have to figure out a lot of stuff if you have problems with lemmy. Thats not okay.
But as always with foss. If you run a public instance, you should accept donations and if they dont cover the costs so you can pay someone to make a fork for you that has what you need, you might be doing something wrong.