The link they chose for lemmy is … interesting. Not quite sure what they’re trying to say with it, is it their own personal account?

The data loss issue definitely applies to Lemmy, indeed. Sure you can use tools to archive your content, but it’s still effort and only easily possible if the instance announces that they’re going to go down - if the instance has a single point of failure and that person is suddenly gone (death, illness, lemmy drama …), you might not be able to do that. And the churn can be quite substantial depending on your choice of instances. And TBH it feels a little absurd to set up an automated backup method for your Lemmy activity.