To stop scrappers, offer the same pricing as API to anyone using the web version of reddit. (New or old doesn't matter.) Ordinary users have to pay, per thousand comments, to see reddit.
Actually, do the same thing with the official app (since folks could otherwise use it for free and take screenshots or something). But leave the ads in too.
As others have said, PDS is a good choice as it avoids a need to use the API. (It does depend on old dot reddit dot com however, but that's not going away tomorrow.)
In short you need to request and get the GDPR/CCPA archive from reddit to make sure you wipe everything. (Some folks can live with just wiping out their top posts and comments however, for which PDS is perfectly fine.)
The downside is that afaik there's no way to feed that archive to PDS. You'll need to use an API using script like shreddit to edit everything.
Reddit admins using that "feature" to post under other usernames perhaps? I dunno if there's a way to check but I wouldn't be surprised if these folks were not actually subbed to the sub that they seem to care so much about.
TLDR reddit might not be restoring data that the user deleted, but there are some funky cases where it's easy to miss stuff when deleting manually. Which is exactly why Update #1 is so bad - it's basically impossible to delete everything without reddit's help.
The other thing to keep in mind is that looks can be deceiving. Reddit has had over half a month to clean up things like r/all from the fallout of the protests.