For a while it seemed that while this was true, edits were at least destructive: so a lot of mass-deletion tools would edit the comments, then optionally delete them. But I wouldn't be surprised if this is no longer the case (TBH, making the edit history of comments public is a good idea in general).
I disagree. Making edit history public would turn the discussion into a total shitshow. Reddit would drown in stuff like: "I see from your second edit you said ... so clearly you're a ignoramus and a bigot."
Delete Suite's main feature is actually that it edits your comment to be junk, rather than just deleting it. I come across some corpses linking to it every now and then.
You could argue that it's not the comments themselves that are personally identifiable, but the association between comment and username (and IP etc). Following that argument, you could retain the comments as long as you delete the username and other identifying info.
Not sure if that would hold up, as some comments can be pretty identifying. But it's a compromise that a company could try.
If i wrote public forum software, that's how I would do it and batch delete only comments that no one asked to undelete in at least a few months...