From Lemmy documentation:
We don’t delete anything from our database, just hide it from users. Deleted or removed Communities/Posts/Comments have a “restore” button.
But don’t take my word for it. Try it out yourself. You can make a comment, delete the comment (your username appears to remain) and then restore its content.
Reddit is even worse. When you delete your comment, it’s not really deleted and still visible to the mods of the sub
That is not true.
No, if a user deletes their comment on Reddit, it is visible only to admins, not to mods. If a mod deletes a user’s comment, it is visible to mod and user, and even on that user’s account page. If an account is deleted, still all the data is retained by Reddit admins.