I have been on reddit for just about 12 years now. Something I've noticed over time is just how hateful the place has become. A complete outrage machine. Every single sub became filled with it. I've filtered so many subreddits over the last few years, it's insane. I don't know enough about this place to be sure, but I do hope it doesn't become the same type of echo chamber of anger.
What's great about Lemmy is that it isn't just one big community but a bunch of small ones that band together to share content. If a community gets too toxic there's a migration path to a new one without getting locked out of the system as a whole.
Back in the old days of the internet when a forum started to get too big they often started to get toxic. Since each forum was isolated leaving it would be pretty hard since you'd not want to lose the good with the bad. Lemmy improves in that in that you can leave for a new community but you don't get locked out of all the content from elsewhere so there's less lock in giving users more choice to find a community that works for them.
One thing that would help is account linking which would decrease lock in even more.
Yes. This is a big potential problem. If you invest a lot of time building up a profile and gaining trust and social cred, you should be able to migrate your profile over to another instance if there are issues